view CONTRIBUTORS @ 39515:93486cc46125

treemanifest: introduce lazy loading of subdirs

An earlier patch series made it so that what to load was up to the calling code,
which works fine until manifests are copied - when they're copied, they're
loaded completely and thus we lose the entire benefit.

By lazy loading everything, we can avoid having to pass in the matcher to ~every
manifest function, and handle copies correctly as well. This changeset doesn't
go as far as it could with loading only the necessary subsets, that will happen
in later changes in this series; at the moment, except in a few situations, we
just load everything the moment we want to interact with treemanifest._dirs.
This is thus most likely to be a small slowdown if treemanifests is in use
regardless of whether narrow is in use, but hopefully easier to verify
correctness and review.

This is part of a series of speedups, it is not expected to produce any real speed
improvements itself, but the numbers show that it doesn't produce a large speed
penalty in any common case, and for the cases it does provide a penalty in, it
is not a large absolute amount (even if it is a large percentage amount).

Timing numbers according to command:

    hyperfine --prepare <preparation_script> 'hg status'

HGRCPATH points to a file with the following contents:

    [extensions]
    narrow =
    strip =
    rebase =

mozilla-unified (called m-u below) was at revision #468856.
        regular hash: eb39298e432d
  treemanifests hash: 0553b7f29eaf

large-dir-repo (called l-d-r below) was generated with the following script:

    #!/bin/bash
    hg init large-dir-repo
    mkdir -p large-dir-repo/third_party/rust/log
    touch large-dir-repo/third_party/rust/log/foo.txt
    for i in $(seq 1 30000); do
        d=$(mktemp -d large-dir-repo/third_party/XXXXXXXXX)
        touch $d/file.txt
    done
    hg -R large-dir-repo ci -Am 'rev0' --user test --date '0 0'
    echo hi > large-dir-repo/third_party/rust/log/bar.txt
    hg -R large-dir-repo ci -Am 'rev1' --user test --date '0 0'
    echo hi > large-dir-repo/third_party/rust/log/baz.txt
    hg -R large-dir-repo ci -Am 'rev2' --user test --date '0 0'

for the repos that use narrow, the narrowspec was this:

    [include]
    rootfilesin:accessible/jsat
    rootfilesin:accessible/tests/mochitest/jsat
    rootfilesin:mobile/android/chrome/content
    rootfilesin:mobile/android/modules/geckoview
    rootfilesin:third_party/rust/log
    [exclude]

This narrowspec was chosen due to the size of the third_party/rust directory
(this directory was *not* modified in revision #468856 in mozilla-unified),
plus all the directories that *were* modified in revision #468856 of
mozilla-unified.

Importantly, when using narrow, these repos had everything checked out (in the
case of large-dir-repo, that means all 30,001 directories), *before* adding the
narrowspec. This is to simulate the behavior when using a virtual filesystem
that shows everything for the user even if they haven't added it to the
narrowspec yet. This is not a supported configuration, and `hg update` and `hg
rebase` will not really do the "correct" thing if there are mutations outside
of the narrowspec (which is not the case in these tests, due to a carefully
crafted narrowspec), but non-mutating commands should behave correctly.

I'm not claiming anything less than a 5% speed win as improvements due to this
change; these are probably eiter measurement artifacts or constant time
improvements. The numbers that aren't changing are shown primarily to prove that
this doesn't make anything worse in any case I plan on testing during this
series.

'before' is hg from commit 6268fed3
'N' indicates narrow in use
'T' indicates treemanifest in use

Please note that these commands and the narrowspec are a little different than
the ones in a similar table that I made in a3cabe9415e1.

Important: it is my understanding that these numbers below are *not super reliable*,
the large slowdowns may be artifacts of some odd interaction between GC and
python module/code complexity. Another changeset of mine (D4351) had shown large
timing differences when ~empty, uncalled functions were added to match.py,
though only when using --color=never or redirecting to /dev/null. We seem to be
on some cusp of complexity or code size that is causing, at my best guess
(according to linux `perf` benchmarks) GC to alter behavior and cause a
200-400ms difference in timings. I haven't had a chance to replicate these
results on another machine.

    diff --git:
    repo  | N | T | before (mean +- stdev) | after (mean +- stdev) | % of before
    ------+---+---+------------------------+-----------------------+------------
    m-u   |   |   | 1.580 s +-  0.034 s    | 1.576 s +-  0.022 s   |  99.7%
    m-u   |   | x | 1.568 s +-  0.025 s    | 1.584 s +-  0.044 s   | 101.0%
    m-u   | x |   | 1.569 s +-  0.031 s    | 1.554 s +-  0.025 s   |  99.0%
    m-u   | x | x | 107.3 ms +-   1.6 ms   | 106.3 ms +-   1.5 ms  |  99.1%
    l-d-r |   |   | 232.5 ms +-   5.9 ms   | 233.5 ms +-   5.3 ms  | 100.4%
    l-d-r |   | x | 236.6 ms +-   6.3 ms   | 233.6 ms +-   7.0 ms  |  98.7%
    l-d-r | x |   | 118.4 ms +-   2.1 ms   | 118.4 ms +-   1.4 ms  | 100.0%
    l-d-r | x | x | 116.8 ms +-   1.5 ms   | 118.9 ms +-   1.6 ms  | 101.8%

    diff -c . --git:
    repo  | N | T | before (mean +- stdev) | after (mean +- stdev) | % of before
    ------+---+---+------------------------+-----------------------+------------
    m-u   |   |   | 354.4 ms +-  16.6 ms   | 351.0 ms +-   6.9 ms  |  99.0%
    m-u   |   | x | 207.2 ms +-   3.0 ms   | 206.2 ms +-   2.7 ms  |  99.5%
    m-u   | x |   | 422.0 ms +-  26.0 ms   | 351.2 ms +-   6.4 ms  |  83.2% <--
    m-u   | x | x | 166.7 ms +-   2.1 ms   | 169.5 ms +-   4.1 ms  | 101.7%
    l-d-r |   |   | 98.4 ms +-   4.5 ms    | 98.5 ms +-   2.1 ms   | 100.1%
    l-d-r |   | x | 5.519 s +-  0.060 s    | 5.149 s +-  0.042 s   |  93.3% <--
    l-d-r | x |   | 99.1 ms +-   3.2 ms    | 102.6 ms +-   9.7 ms  | 103.5% <--?
    l-d-r | x | x | 994.9 ms +-  10.7 ms   | 1.026 s +-  0.012 s   | 103.1% <--?

    rebase -r . --keep -d .^^:
    repo  | N | T | before (mean +- stdev) | after (mean +- stdev) | % of before
    ------+---+---+------------------------+-----------------------+------------
    m-u   |   |   | 6.639 s +-  0.168 s    | 6.559 s +-  0.097 s   |  98.8%
    m-u   |   | x | 6.601 s +-  0.143 s    | 6.640 s +-  0.207 s   | 100.6%
    m-u   | x |   | 6.582 s +-  0.098 s    | 6.543 s +-  0.098 s   |  99.4%
    m-u   | x | x | 678.4 ms +-  57.7 ms   | 703.7 ms +-  52.4 ms  | 103.7% <--?
    l-d-r |   |   | 780.0 ms +-  23.9 ms   | 776.0 ms +-  12.6 ms  |  99.5%
    l-d-r |   | x | 7.520 s +-  0.255 s    | 7.395 s +-  0.044 s   |  98.3%
    l-d-r | x |   | 331.9 ms +-  16.5 ms   | 327.0 ms +-   3.4 ms  |  98.5%
    l-d-r | x | x | 6.228 s +-  0.113 s    | 5.924 s +-  0.044 s   |  95.1%

    status --change . --copies:
    repo  | N | T | before (mean +- stdev) | after (mean +- stdev) | % of before
    ------+---+---+------------------------+-----------------------+------------
    m-u   |   |   | 330.8 ms +-   7.2 ms   | 329.0 ms +-   7.1 ms  |  99.5%
    m-u   |   | x | 182.9 ms +-   2.7 ms   | 183.5 ms +-   2.7 ms  | 100.3%
    m-u   | x |   | 330.0 ms +-   7.6 ms   | 327.1 ms +-   5.4 ms  |  99.1%
    m-u   | x | x | 146.2 ms +-   2.4 ms   | 147.1 ms +-   1.3 ms  | 100.6%
    l-d-r |   |   | 95.3 ms +-   1.4 ms    | 95.9 ms +-   1.5 ms   | 100.6%
    l-d-r |   | x | 5.157 s +-  0.035 s    | 5.166 s +-  0.058 s   | 100.2%
    l-d-r | x |   | 99.7 ms +-   3.0 ms    | 100.2 ms +-   4.4 ms  | 100.5%
    l-d-r | x | x | 993.6 ms +-  13.1 ms   | 1.025 s +-  0.015 s   | 103.2% <--?

    status --copies:
    repo  | N | T | before (mean +- stdev) | after (mean +- stdev) | % of before
    ------+---+---+------------------------+-----------------------+------------
    m-u   |   |   | 2.348 s +-  0.031 s    | 2.329 s +-  0.019 s   |  99.2%
    m-u   |   | x | 2.337 s +-  0.026 s    | 2.346 s +-  0.034 s   | 100.4%
    m-u   | x |   | 2.354 s +-  0.015 s    | 2.342 s +-  0.021 s   |  99.5%
    m-u   | x | x | 120.6 ms +-   4.3 ms   | 119.2 ms +-   2.1 ms  |  98.8%
    l-d-r |   |   | 731.5 ms +-  11.1 ms   | 719.6 ms +-   9.8 ms  |  98.4%
    l-d-r |   | x | 729.0 ms +-  15.5 ms   | 725.7 ms +-  10.6 ms  |  99.5%
    l-d-r | x |   | 211.0 ms +-   3.9 ms   | 212.8 ms +-   3.7 ms  | 100.9%
    l-d-r | x | x | 211.5 ms +-   4.2 ms   | 211.0 ms +-   3.3 ms  |  99.8%

    update $rev^; ~/src/hg/hg{hg}/hg update $rev:
    repo  | N | T | before (mean +- stdev) | after (mean +- stdev) | % of before
    ------+---+---+------------------------+-----------------------+------------
    m-u   |   |   | 3.910 s +-  0.055 s    | 3.920 s +-  0.075 s   | 100.3%
    m-u   |   | x | 3.613 s +-  0.056 s    | 3.630 s +-  0.056 s   | 100.5%
    m-u   | x |   | 3.873 s +-  0.055 s    | 3.864 s +-  0.049 s   |  99.8%
    m-u   | x | x | 400.4 ms +-   7.4 ms   | 403.6 ms +-   5.0 ms  | 100.8%
    l-d-r |   |   | 531.6 ms +-  10.0 ms   | 528.8 ms +-   9.6 ms  |  99.5%
    l-d-r |   | x | 10.377 s +-  0.049 s   | 9.955 s +-  0.046 s   |  95.9%
    l-d-r | x |   | 308.3 ms +-   4.4 ms   | 306.8 ms +-   3.7 ms  |  99.5%
    l-d-r | x | x | 1.805 s +-  0.015 s    | 1.834 s +-  0.020 s   | 101.6%

Differential Revision: https://phab.mercurial-scm.org/D4366

[This file is here for historical purposes, all recent contributors
should appear in the changelog directly]

Andrea Arcangeli <andrea at suse.de>
Thomas Arendsen Hein <thomas at intevation.de>
Goffredo Baroncelli <kreijack at libero.it>
Muli Ben-Yehuda <mulix at mulix.org>
Mikael Berthe <mikael at lilotux.net>
Benoit Boissinot <bboissin at gmail.com>
Brendan Cully <brendan at kublai.com>
Vincent Danjean <vdanjean.ml at free.fr>
Jake Edge <jake at edge2.net>
Michael Fetterman <michael.fetterman at intel.com>
Edouard Gomez <ed.gomez at free.fr>
Eric Hopper <hopper at omnifarious.org>
Alecs King <alecsk at gmail.com>
Volker Kleinfeld <Volker.Kleinfeld at gmx.de>
Vadim Lebedev <vadim at mbdsys.com>
Christopher Li <hg at chrisli.org>
Chris Mason <mason at suse.com>
Colin McMillen <mcmillen at cs.cmu.edu>
Wojciech Milkowski <wmilkowski at interia.pl>
Chad Netzer <chad.netzer at gmail.com>
Bryan O'Sullivan <bos at serpentine.com>
Vicent Seguí Pascual <vseguip at gmail.com>
Sean Perry <shaleh at speakeasy.net>
Nguyen Anh Quynh <aquynh at gmail.com>
Ollivier Robert <roberto at keltia.freenix.fr>
Alexander Schremmer <alex at alexanderweb.de>
Arun Sharma <arun at sharma-home.net>
Josef "Jeff" Sipek <jeffpc at optonline.net>
Kevin Smith <yarcs at qualitycode.com>
TK Soh <teekaysoh at yahoo.com>
Radoslaw Szkodzinski <astralstorm at gorzow.mm.pl>
Samuel Tardieu <sam at rfc1149.net>
K Thananchayan <thananck at yahoo.com>
Andrew Thompson <andrewkt at aktzero.com>
Michael S. Tsirkin <mst at mellanox.co.il>
Rafael Villar Burke <pachi at mmn-arquitectos.com>
Tristan Wibberley <tristan at wibberley.org>
Mark Williamson <mark.williamson at cl.cam.ac.uk>