1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
//! # Rust Compiler Self-Profiling
//!
//! This module implements the basic framework for the compiler's self-
//! profiling support. It provides the `SelfProfiler` type which enables
//! recording "events". An event is something that starts and ends at a given
//! point in time and has an ID and a kind attached to it. This allows for
//! tracing the compiler's activity.
//!
//! Internally this module uses the custom tailored [measureme][mm] crate for
//! efficiently recording events to disk in a compact format that can be
//! post-processed and analyzed by the suite of tools in the `measureme`
//! project. The highest priority for the tracing framework is on incurring as
//! little overhead as possible.
//!
//!
//! ## Event Overview
//!
//! Events have a few properties:
//!
//! - The `event_kind` designates the broad category of an event (e.g. does it
//!   correspond to the execution of a query provider or to loading something
//!   from the incr. comp. on-disk cache, etc).
//! - The `event_id` designates the query invocation or function call it
//!   corresponds to, possibly including the query key or function arguments.
//! - Each event stores the ID of the thread it was recorded on.
//! - The timestamp stores beginning and end of the event, or the single point
//!   in time it occurred at for "instant" events.
//!
//!
//! ## Event Filtering
//!
//! Event generation can be filtered by event kind. Recording all possible
//! events generates a lot of data, much of which is not needed for most kinds
//! of analysis. So, in order to keep overhead as low as possible for a given
//! use case, the `SelfProfiler` will only record the kinds of events that
//! pass the filter specified as a command line argument to the compiler.
//!
//!
//! ## `event_id` Assignment
//!
//! As far as `measureme` is concerned, `event_id`s are just strings. However,
//! it would incur too much overhead to generate and persist each `event_id`
//! string at the point where the event is recorded. In order to make this more
//! efficient `measureme` has two features:
//!
//! - Strings can share their content, so that re-occurring parts don't have to
//!   be copied over and over again. One allocates a string in `measureme` and
//!   gets back a `StringId`. This `StringId` is then used to refer to that
//!   string. `measureme` strings are actually DAGs of string components so that
//!   arbitrary sharing of substrings can be done efficiently. This is useful
//!   because `event_id`s contain lots of redundant text like query names or
//!   def-path components.
//!
//! - `StringId`s can be "virtual" which means that the client picks a numeric
//!   ID according to some application-specific scheme and can later make that
//!   ID be mapped to an actual string. This is used to cheaply generate
//!   `event_id`s while the events actually occur, causing little timing
//!   distortion, and then later map those `StringId`s, in bulk, to actual
//!   `event_id` strings. This way the largest part of the tracing overhead is
//!   localized to one contiguous chunk of time.
//!
//! How are these `event_id`s generated in the compiler? For things that occur
//! infrequently (e.g. "generic activities"), we just allocate the string the
//! first time it is used and then keep the `StringId` in a hash table. This
//! is implemented in `SelfProfiler::get_or_alloc_cached_string()`.
//!
//! For queries it gets more interesting: First we need a unique numeric ID for
//! each query invocation (the `QueryInvocationId`). This ID is used as the
//! virtual `StringId` we use as `event_id` for a given event. This ID has to
//! be available both when the query is executed and later, together with the
//! query key, when we allocate the actual `event_id` strings in bulk.
//!
//! We could make the compiler generate and keep track of such an ID for each
//! query invocation but luckily we already have something that fits all the
//! the requirements: the query's `DepNodeIndex`. So we use the numeric value
//! of the `DepNodeIndex` as `event_id` when recording the event and then,
//! just before the query context is dropped, we walk the entire query cache
//! (which stores the `DepNodeIndex` along with the query key for each
//! invocation) and allocate the corresponding strings together with a mapping
//! for `DepNodeIndex as StringId`.
//!
//! [mm]: https://github.com/rust-lang/measureme/

use crate::cold_path;
use crate::fx::FxHashMap;

use std::borrow::Borrow;
use std::collections::hash_map::Entry;
use std::convert::Into;
use std::error::Error;
use std::fs;
use std::path::Path;
use std::process;
use std::sync::Arc;
use std::time::{Duration, Instant};
use std::u32;

use measureme::{EventId, EventIdBuilder, SerializableString, StringId};
use parking_lot::RwLock;

/// MmapSerializatioSink is faster on macOS and Linux
/// but FileSerializationSink is faster on Windows
#[cfg(not(windows))]
type SerializationSink = measureme::MmapSerializationSink;
#[cfg(windows)]
type SerializationSink = measureme::FileSerializationSink;

type Profiler = measureme::Profiler<SerializationSink>;

#[derive(Clone, Copy, Debug, PartialEq, Eq, Ord, PartialOrd)]
pub enum ProfileCategory {
    Parsing,
    Expansion,
    TypeChecking,
    BorrowChecking,
    Codegen,
    Linking,
    Other,
}

bitflags::bitflags! {
    struct EventFilter: u32 {
        const GENERIC_ACTIVITIES = 1 << 0;
        const QUERY_PROVIDERS    = 1 << 1;
        const QUERY_CACHE_HITS   = 1 << 2;
        const QUERY_BLOCKED      = 1 << 3;
        const INCR_CACHE_LOADS   = 1 << 4;

        const QUERY_KEYS         = 1 << 5;
        const FUNCTION_ARGS      = 1 << 6;
        const LLVM               = 1 << 7;

        const DEFAULT = Self::GENERIC_ACTIVITIES.bits |
                        Self::QUERY_PROVIDERS.bits |
                        Self::QUERY_BLOCKED.bits |
                        Self::INCR_CACHE_LOADS.bits;

        const ARGS = Self::QUERY_KEYS.bits | Self::FUNCTION_ARGS.bits;
    }
}

// keep this in sync with the `-Z self-profile-events` help message in librustc_session/options.rs
const EVENT_FILTERS_BY_NAME: &[(&str, EventFilter)] = &[
    ("none", EventFilter::empty()),
    ("all", EventFilter::all()),
    ("default", EventFilter::DEFAULT),
    ("generic-activity", EventFilter::GENERIC_ACTIVITIES),
    ("query-provider", EventFilter::QUERY_PROVIDERS),
    ("query-cache-hit", EventFilter::QUERY_CACHE_HITS),
    ("query-blocked", EventFilter::QUERY_BLOCKED),
    ("incr-cache-load", EventFilter::INCR_CACHE_LOADS),
    ("query-keys", EventFilter::QUERY_KEYS),
    ("function-args", EventFilter::FUNCTION_ARGS),
    ("args", EventFilter::ARGS),
    ("llvm", EventFilter::LLVM),
];

/// Something that uniquely identifies a query invocation.
pub struct QueryInvocationId(pub u32);

/// A reference to the SelfProfiler. It can be cloned and sent across thread
/// boundaries at will.
#[derive(Clone)]
pub struct SelfProfilerRef {
    // This field is `None` if self-profiling is disabled for the current
    // compilation session.
    profiler: Option<Arc<SelfProfiler>>,

    // We store the filter mask directly in the reference because that doesn't
    // cost anything and allows for filtering with checking if the profiler is
    // actually enabled.
    event_filter_mask: EventFilter,

    // Print verbose generic activities to stdout
    print_verbose_generic_activities: bool,

    // Print extra verbose generic activities to stdout
    print_extra_verbose_generic_activities: bool,
}

impl SelfProfilerRef {
    pub fn new(
        profiler: Option<Arc<SelfProfiler>>,
        print_verbose_generic_activities: bool,
        print_extra_verbose_generic_activities: bool,
    ) -> SelfProfilerRef {
        // If there is no SelfProfiler then the filter mask is set to NONE,
        // ensuring that nothing ever tries to actually access it.
        let event_filter_mask =
            profiler.as_ref().map(|p| p.event_filter_mask).unwrap_or(EventFilter::empty());

        SelfProfilerRef {
            profiler,
            event_filter_mask,
            print_verbose_generic_activities,
            print_extra_verbose_generic_activities,
        }
    }

    // This shim makes sure that calls only get executed if the filter mask
    // lets them pass. It also contains some trickery to make sure that
    // code is optimized for non-profiling compilation sessions, i.e. anything
    // past the filter check is never inlined so it doesn't clutter the fast
    // path.
    #[inline(always)]
    fn exec<F>(&self, event_filter: EventFilter, f: F) -> TimingGuard<'_>
    where
        F: for<'a> FnOnce(&'a SelfProfiler) -> TimingGuard<'a>,
    {
        #[inline(never)]
        fn cold_call<F>(profiler_ref: &SelfProfilerRef, f: F) -> TimingGuard<'_>
        where
            F: for<'a> FnOnce(&'a SelfProfiler) -> TimingGuard<'a>,
        {
            let profiler = profiler_ref.profiler.as_ref().unwrap();
            f(&**profiler)
        }

        if unlikely!(self.event_filter_mask.contains(event_filter)) {
            cold_call(self, f)
        } else {
            TimingGuard::none()
        }
    }

    /// Start profiling a verbose generic activity. Profiling continues until the
    /// VerboseTimingGuard returned from this call is dropped. In addition to recording
    /// a measureme event, "verbose" generic activities also print a timing entry to
    /// stdout if the compiler is invoked with -Ztime or -Ztime-passes.
    pub fn verbose_generic_activity<'a>(
        &'a self,
        event_label: &'static str,
    ) -> VerboseTimingGuard<'a> {
        let message =
            if self.print_verbose_generic_activities { Some(event_label.to_owned()) } else { None };

        VerboseTimingGuard::start(message, self.generic_activity(event_label))
    }

    /// Start profiling a extra verbose generic activity. Profiling continues until the
    /// VerboseTimingGuard returned from this call is dropped. In addition to recording
    /// a measureme event, "extra verbose" generic activities also print a timing entry to
    /// stdout if the compiler is invoked with -Ztime-passes.
    pub fn extra_verbose_generic_activity<'a, A>(
        &'a self,
        event_label: &'static str,
        event_arg: A,
    ) -> VerboseTimingGuard<'a>
    where
        A: Borrow<str> + Into<String>,
    {
        let message = if self.print_extra_verbose_generic_activities {
            Some(format!("{}({})", event_label, event_arg.borrow()))
        } else {
            None
        };

        VerboseTimingGuard::start(message, self.generic_activity_with_arg(event_label, event_arg))
    }

    /// Start profiling a generic activity. Profiling continues until the
    /// TimingGuard returned from this call is dropped.
    #[inline(always)]
    pub fn generic_activity(&self, event_label: &'static str) -> TimingGuard<'_> {
        self.exec(EventFilter::GENERIC_ACTIVITIES, |profiler| {
            let event_label = profiler.get_or_alloc_cached_string(event_label);
            let event_id = EventId::from_label(event_label);
            TimingGuard::start(profiler, profiler.generic_activity_event_kind, event_id)
        })
    }

    /// Start profiling a generic activity. Profiling continues until the
    /// TimingGuard returned from this call is dropped.
    #[inline(always)]
    pub fn generic_activity_with_arg<A>(
        &self,
        event_label: &'static str,
        event_arg: A,
    ) -> TimingGuard<'_>
    where
        A: Borrow<str> + Into<String>,
    {
        self.exec(EventFilter::GENERIC_ACTIVITIES, |profiler| {
            let builder = EventIdBuilder::new(&profiler.profiler);
            let event_label = profiler.get_or_alloc_cached_string(event_label);
            let event_id = if profiler.event_filter_mask.contains(EventFilter::FUNCTION_ARGS) {
                let event_arg = profiler.get_or_alloc_cached_string(event_arg);
                builder.from_label_and_arg(event_label, event_arg)
            } else {
                builder.from_label(event_label)
            };
            TimingGuard::start(profiler, profiler.generic_activity_event_kind, event_id)
        })
    }

    /// Start profiling a query provider. Profiling continues until the
    /// TimingGuard returned from this call is dropped.
    #[inline(always)]
    pub fn query_provider(&self) -> TimingGuard<'_> {
        self.exec(EventFilter::QUERY_PROVIDERS, |profiler| {
            TimingGuard::start(profiler, profiler.query_event_kind, EventId::INVALID)
        })
    }

    /// Record a query in-memory cache hit.
    #[inline(always)]
    pub fn query_cache_hit(&self, query_invocation_id: QueryInvocationId) {
        self.instant_query_event(
            |profiler| profiler.query_cache_hit_event_kind,
            query_invocation_id,
            EventFilter::QUERY_CACHE_HITS,
        );
    }

    /// Start profiling a query being blocked on a concurrent execution.
    /// Profiling continues until the TimingGuard returned from this call is
    /// dropped.
    #[inline(always)]
    pub fn query_blocked(&self) -> TimingGuard<'_> {
        self.exec(EventFilter::QUERY_BLOCKED, |profiler| {
            TimingGuard::start(profiler, profiler.query_blocked_event_kind, EventId::INVALID)
        })
    }

    /// Start profiling how long it takes to load a query result from the
    /// incremental compilation on-disk cache. Profiling continues until the
    /// TimingGuard returned from this call is dropped.
    #[inline(always)]
    pub fn incr_cache_loading(&self) -> TimingGuard<'_> {
        self.exec(EventFilter::INCR_CACHE_LOADS, |profiler| {
            TimingGuard::start(
                profiler,
                profiler.incremental_load_result_event_kind,
                EventId::INVALID,
            )
        })
    }

    #[inline(always)]
    fn instant_query_event(
        &self,
        event_kind: fn(&SelfProfiler) -> StringId,
        query_invocation_id: QueryInvocationId,
        event_filter: EventFilter,
    ) {
        drop(self.exec(event_filter, |profiler| {
            let event_id = StringId::new_virtual(query_invocation_id.0);
            let thread_id = std::thread::current().id().as_u64() as u32;

            profiler.profiler.record_instant_event(
                event_kind(profiler),
                EventId::from_virtual(event_id),
                thread_id,
            );

            TimingGuard::none()
        }));
    }

    pub fn with_profiler(&self, f: impl FnOnce(&SelfProfiler)) {
        if let Some(profiler) = &self.profiler {
            f(&profiler)
        }
    }

    #[inline]
    pub fn enabled(&self) -> bool {
        self.profiler.is_some()
    }

    #[inline]
    pub fn llvm_recording_enabled(&self) -> bool {
        self.event_filter_mask.contains(EventFilter::LLVM)
    }
    #[inline]
    pub fn get_self_profiler(&self) -> Option<Arc<SelfProfiler>> {
        self.profiler.clone()
    }
}

pub struct SelfProfiler {
    profiler: Profiler,
    event_filter_mask: EventFilter,

    string_cache: RwLock<FxHashMap<String, StringId>>,

    query_event_kind: StringId,
    generic_activity_event_kind: StringId,
    incremental_load_result_event_kind: StringId,
    query_blocked_event_kind: StringId,
    query_cache_hit_event_kind: StringId,
}

impl SelfProfiler {
    pub fn new(
        output_directory: &Path,
        crate_name: Option<&str>,
        event_filters: &Option<Vec<String>>,
    ) -> Result<SelfProfiler, Box<dyn Error>> {
        fs::create_dir_all(output_directory)?;

        let crate_name = crate_name.unwrap_or("unknown-crate");
        let filename = format!("{}-{}.rustc_profile", crate_name, process::id());
        let path = output_directory.join(&filename);
        let profiler = Profiler::new(&path)?;

        let query_event_kind = profiler.alloc_string("Query");
        let generic_activity_event_kind = profiler.alloc_string("GenericActivity");
        let incremental_load_result_event_kind = profiler.alloc_string("IncrementalLoadResult");
        let query_blocked_event_kind = profiler.alloc_string("QueryBlocked");
        let query_cache_hit_event_kind = profiler.alloc_string("QueryCacheHit");

        let mut event_filter_mask = EventFilter::empty();

        if let Some(ref event_filters) = *event_filters {
            let mut unknown_events = vec![];
            for item in event_filters {
                if let Some(&(_, mask)) =
                    EVENT_FILTERS_BY_NAME.iter().find(|&(name, _)| name == item)
                {
                    event_filter_mask |= mask;
                } else {
                    unknown_events.push(item.clone());
                }
            }

            // Warn about any unknown event names
            if unknown_events.len() > 0 {
                unknown_events.sort();
                unknown_events.dedup();

                warn!(
                    "Unknown self-profiler events specified: {}. Available options are: {}.",
                    unknown_events.join(", "),
                    EVENT_FILTERS_BY_NAME
                        .iter()
                        .map(|&(name, _)| name.to_string())
                        .collect::<Vec<_>>()
                        .join(", ")
                );
            }
        } else {
            event_filter_mask = EventFilter::DEFAULT;
        }

        Ok(SelfProfiler {
            profiler,
            event_filter_mask,
            string_cache: RwLock::new(FxHashMap::default()),
            query_event_kind,
            generic_activity_event_kind,
            incremental_load_result_event_kind,
            query_blocked_event_kind,
            query_cache_hit_event_kind,
        })
    }

    /// Allocates a new string in the profiling data. Does not do any caching
    /// or deduplication.
    pub fn alloc_string<STR: SerializableString + ?Sized>(&self, s: &STR) -> StringId {
        self.profiler.alloc_string(s)
    }

    /// Gets a `StringId` for the given string. This method makes sure that
    /// any strings going through it will only be allocated once in the
    /// profiling data.
    pub fn get_or_alloc_cached_string<A>(&self, s: A) -> StringId
    where
        A: Borrow<str> + Into<String>,
    {
        // Only acquire a read-lock first since we assume that the string is
        // already present in the common case.
        {
            let string_cache = self.string_cache.read();

            if let Some(&id) = string_cache.get(s.borrow()) {
                return id;
            }
        }

        let mut string_cache = self.string_cache.write();
        // Check if the string has already been added in the small time window
        // between dropping the read lock and acquiring the write lock.
        match string_cache.entry(s.into()) {
            Entry::Occupied(e) => *e.get(),
            Entry::Vacant(e) => {
                let string_id = self.profiler.alloc_string(&e.key()[..]);
                *e.insert(string_id)
            }
        }
    }

    pub fn map_query_invocation_id_to_string(&self, from: QueryInvocationId, to: StringId) {
        let from = StringId::new_virtual(from.0);
        self.profiler.map_virtual_to_concrete_string(from, to);
    }

    pub fn bulk_map_query_invocation_id_to_single_string<I>(&self, from: I, to: StringId)
    where
        I: Iterator<Item = QueryInvocationId> + ExactSizeIterator,
    {
        let from = from.map(|qid| StringId::new_virtual(qid.0));
        self.profiler.bulk_map_virtual_to_single_concrete_string(from, to);
    }

    pub fn query_key_recording_enabled(&self) -> bool {
        self.event_filter_mask.contains(EventFilter::QUERY_KEYS)
    }

    pub fn event_id_builder(&self) -> EventIdBuilder<'_, SerializationSink> {
        EventIdBuilder::new(&self.profiler)
    }
}

#[must_use]
pub struct TimingGuard<'a>(Option<measureme::TimingGuard<'a, SerializationSink>>);

impl<'a> TimingGuard<'a> {
    #[inline]
    pub fn start(
        profiler: &'a SelfProfiler,
        event_kind: StringId,
        event_id: EventId,
    ) -> TimingGuard<'a> {
        let thread_id = std::thread::current().id().as_u64() as u32;
        let raw_profiler = &profiler.profiler;
        let timing_guard =
            raw_profiler.start_recording_interval_event(event_kind, event_id, thread_id);
        TimingGuard(Some(timing_guard))
    }

    #[inline]
    pub fn finish_with_query_invocation_id(self, query_invocation_id: QueryInvocationId) {
        if let Some(guard) = self.0 {
            cold_path(|| {
                let event_id = StringId::new_virtual(query_invocation_id.0);
                let event_id = EventId::from_virtual(event_id);
                guard.finish_with_override_event_id(event_id);
            });
        }
    }

    #[inline]
    pub fn none() -> TimingGuard<'a> {
        TimingGuard(None)
    }

    #[inline(always)]
    pub fn run<R>(self, f: impl FnOnce() -> R) -> R {
        let _timer = self;
        f()
    }
}

#[must_use]
pub struct VerboseTimingGuard<'a> {
    start_and_message: Option<(Instant, String)>,
    _guard: TimingGuard<'a>,
}

impl<'a> VerboseTimingGuard<'a> {
    pub fn start(message: Option<String>, _guard: TimingGuard<'a>) -> Self {
        VerboseTimingGuard { _guard, start_and_message: message.map(|msg| (Instant::now(), msg)) }
    }

    #[inline(always)]
    pub fn run<R>(self, f: impl FnOnce() -> R) -> R {
        let _timer = self;
        f()
    }
}

impl Drop for VerboseTimingGuard<'_> {
    fn drop(&mut self) {
        if let Some((start, ref message)) = self.start_and_message {
            print_time_passes_entry(true, &message[..], start.elapsed());
        }
    }
}

pub fn print_time_passes_entry(do_it: bool, what: &str, dur: Duration) {
    if !do_it {
        return;
    }

    let mem_string = match get_resident() {
        Some(n) => {
            let mb = n as f64 / 1_000_000.0;
            format!("; rss: {}MB", mb.round() as usize)
        }
        None => String::new(),
    };
    println!("time: {}{}\t{}", duration_to_secs_str(dur), mem_string, what);
}

// Hack up our own formatting for the duration to make it easier for scripts
// to parse (always use the same number of decimal places and the same unit).
pub fn duration_to_secs_str(dur: std::time::Duration) -> String {
    const NANOS_PER_SEC: f64 = 1_000_000_000.0;
    let secs = dur.as_secs() as f64 + dur.subsec_nanos() as f64 / NANOS_PER_SEC;

    format!("{:.3}", secs)
}

// Memory reporting
#[cfg(unix)]
fn get_resident() -> Option<usize> {
    let field = 1;
    let contents = fs::read("/proc/self/statm").ok()?;
    let contents = String::from_utf8(contents).ok()?;
    let s = contents.split_whitespace().nth(field)?;
    let npages = s.parse::<usize>().ok()?;
    Some(npages * 4096)
}

#[cfg(windows)]
fn get_resident() -> Option<usize> {
    use std::mem::{self, MaybeUninit};
    use winapi::shared::minwindef::DWORD;
    use winapi::um::processthreadsapi::GetCurrentProcess;
    use winapi::um::psapi::{GetProcessMemoryInfo, PROCESS_MEMORY_COUNTERS};

    let mut pmc = MaybeUninit::<PROCESS_MEMORY_COUNTERS>::uninit();
    match unsafe {
        GetProcessMemoryInfo(GetCurrentProcess(), pmc.as_mut_ptr(), mem::size_of_val(&pmc) as DWORD)
    } {
        0 => None,
        _ => {
            let pmc = unsafe { pmc.assume_init() };
            Some(pmc.WorkingSetSize as usize)
        }
    }
}