view tests/test-narrow-clone-no-ellipsis.t @ 51681:522b4d729e89

mmap: populate the mapping by default

Without pre-population, accessing all data through a mmap can result in many
pagefault, reducing performance significantly. If the mmap is prepopulated, the
performance can no longer get slower than a full read.
(See benchmark number below)

In some cases were very few data is read, prepopulating can be overkill and
slower than populating on access (through page fault). So that behavior can be
controlled when the caller can pre-determine the best behavior.
(See benchmark number below)

In addition, testing with populating in a secondary thread yield great result
combining the best of each approach. This might be implemented in later
changesets.

In all cases, using mmap has a great effect on memory usage when many processes
run in parallel on the same machine.

### Benchmarks

# What did I run

A couple of month back I ran a large benchmark campaign to assess the impact of
various approach for using mmap with the revlog (and other files), it
highlighted a few benchmarks that capture the impact of the changes well. So to
validate this change I checked the following:

- log command displaying various revisions
  (read the changelog index)
- log command displaying the patch of listed revisions
  (read the changelog index, the manifest index and a few files indexes)
- unbundling a few revisions
  (read and write changelog, manifest and few files indexes, and walk the graph
  to update some cache)
- pushing a few revisions
  (read and write changelog, manifest and few files indexes, walk the graph to
  update some cache, performs various accesses locally and remotely during
  discovery)

Benchmarks were run using the default module policy (c+py) and the rust one. No
significant difference were found between the two implementation, so we will
present result using the default policy (unless otherwise specified).

I ran them on a few repositories :

- mercurial: a "public changeset only" copy of mercurial from 2018-08-01 using
  zstd compression and sparse-revlog

- pypy: a copy of pypy from 2018-08-01 using zstd compression and sparse-revlog

- netbeans: a copy of netbeans from 2018-08-01 using zstd compression and
  sparse-revlog

- mozilla-try: a copy of mozilla-try from 2019-02-18 using zstd compression and
  sparse-revlog

- mozilla-try persistent-nodemap: Same as the above but with a persistent
  nodemap. Used for the log --patch benchmark only

# Results

For the smaller repositories (mercurial, pypy), the impact of mmap is almost
imperceptible, other cost dominating the operation. The impact of prepopulating
is undiscernible in the benchmark we ran.

For larger repositories the benchmark support explanation given above:

On netbeans, the log can be about 1% faster without repopulation (for a
difference < 100ms) but unbundle becomes a bit slower, even when small.

### data-env-vars.name                             = netbeans-2018-08-01-zstd-sparse-revlog
  # benchmark.name                                 = hg.command.unbundle
  # benchmark.variants.issue6528                   = disabled
  # benchmark.variants.reuse-external-delta-parent = yes
  # benchmark.variants.revs                        = any-1-extra-rev
  # benchmark.variants.source                      = unbundle
  # benchmark.variants.verbosity                   = quiet
with-populate: 0.240157
no-populate:   0.265087  (+10.38%, +0.02)
  # benchmark.variants.revs                        = any-100-extra-rev
with-populate: 1.459518
no-populate:   1.481290   (+1.49%, +0.02)
 ## benchmark.name                                 = hg.command.push
  # benchmark.variants.explicit-rev                = none
  # benchmark.variants.issue6528                   = disabled
  # benchmark.variants.protocol                    = ssh
  # benchmark.variants.reuse-external-delta-parent = yes
  # benchmark.variants.revs                        = any-1-extra-rev
with-populate: 0.771919
no-populate:   0.792025   (+2.60%, +0.02)
  # benchmark.variants.revs                        = any-100-extra-rev
with-populate: 1.459518
no-populate:   1.481290   (+1.49%, +0.02)


For mozilla-try, the "slow down" from pre-populate for small `hg log` is more
visible, but still small in absolute time. (using rust value for the persistent
nodemap value to be relevant).

### data-env-vars.name            = mozilla-try-2019-02-18-ds2-pnm
  # benchmark.name                = hg.command.log
  # bin-env-vars.hg.flavor        = rust
  # benchmark.variants.patch      = yes
  # benchmark.variants.limit-rev  = 1
with-populate: 0.237813
no-populate:   0.229452   (-3.52%, -0.01)
  # benchmark.variants.limit-rev  = 10
  # benchmark.variants.patch      = yes
with-populate: 1.213578
no-populate:   1.205189
### data-env-vars.name            = mozilla-try-2019-02-18-zstd-sparse-revlog
  # benchmark.variants.limit-rev  = 1000
  # benchmark.variants.patch      = no
  # benchmark.variants.rev        = tip
with-populate: 0.198607
no-populate:   0.195038   (-1.80%, -0.00)

However pre-populating provide a significant boost on more complex operations
like unbundle or push:

### data-env-vars.name                             = mozilla-try-2019-02-18-zstd-sparse-revlog
  # benchmark.name                                 = hg.command.push
  # benchmark.variants.explicit-rev                = none
  # benchmark.variants.issue6528                   = disabled
  # benchmark.variants.protocol                    = ssh
  # benchmark.variants.reuse-external-delta-parent = yes
  # benchmark.variants.revs                        = any-1-extra-rev
with-populate: 4.798632
no-populate:   4.953295   (+3.22%, +0.15)
  # benchmark.variants.revs                        = any-100-extra-rev
with-populate: 4.903618
no-populate:   5.014963   (+2.27%, +0.11)
 ## benchmark.name                                 = hg.command.unbundle
  # benchmark.variants.revs                        = any-1-extra-rev
with-populate: 1.423411
no-populate:   1.585365  (+11.38%, +0.16)
  # benchmark.variants.revs                        = any-100-extra-rev
with-populate: 1.537909
no-populate:   1.688489   (+9.79%, +0.15)

  $ . "$TESTDIR/narrow-library.sh"

  $ hg init master
  $ cd master
  $ mkdir dir
  $ mkdir dir/src
  $ cd dir/src
  $ for x in `$TESTDIR/seq.py 20`; do echo $x > "f$x"; hg add "f$x"; hg commit -m "Commit src $x"; done
  $ cd ..
  $ mkdir tests
  $ cd tests
  $ for x in `$TESTDIR/seq.py 20`; do echo $x > "t$x"; hg add "t$x"; hg commit -m "Commit test $x"; done
  $ cd ../../..

narrow clone a file, f10

  $ hg clone --narrow ssh://user@dummy/master narrow --noupdate --include "dir/src/f10"
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 40 changesets with 1 changes to 1 files
  new changesets *:* (glob)
  $ cd narrow
  $ hg debugrequires | grep -v generaldelta
  dotencode
  dirstate-v2 (dirstate-v2 !)
  fncache
  narrowhg-experimental
  persistent-nodemap (rust !)
  revlog-compression-zstd (zstd !)
  revlogv1
  share-safe
  sparserevlog
  store
  testonly-simplestore (reposimplestore !)

  $ hg tracked
  I path:dir/src/f10
  $ hg update
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ find * | sort
  dir
  dir/src
  dir/src/f10
  $ cat dir/src/f10
  10

  $ cd ..

narrow clone a directory, tests/, except tests/t19

  $ hg clone --narrow ssh://user@dummy/master narrowdir --noupdate --include "dir/tests/" --exclude "dir/tests/t19"
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 40 changesets with 19 changes to 19 files
  new changesets *:* (glob)
  $ cd narrowdir
  $ hg tracked
  I path:dir/tests
  X path:dir/tests/t19
  $ hg update
  19 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ find * | sort
  dir
  dir/tests
  dir/tests/t1
  dir/tests/t10
  dir/tests/t11
  dir/tests/t12
  dir/tests/t13
  dir/tests/t14
  dir/tests/t15
  dir/tests/t16
  dir/tests/t17
  dir/tests/t18
  dir/tests/t2
  dir/tests/t20
  dir/tests/t3
  dir/tests/t4
  dir/tests/t5
  dir/tests/t6
  dir/tests/t7
  dir/tests/t8
  dir/tests/t9

  $ cd ..

narrow clone everything but a directory (tests/)

  $ hg clone --narrow ssh://user@dummy/master narrowroot --noupdate --exclude "dir/tests"
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 40 changesets with 20 changes to 20 files
  new changesets *:* (glob)
  $ cd narrowroot
  $ hg tracked
  I path:.
  X path:dir/tests
  $ hg update
  20 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ find * | sort
  dir
  dir/src
  dir/src/f1
  dir/src/f10
  dir/src/f11
  dir/src/f12
  dir/src/f13
  dir/src/f14
  dir/src/f15
  dir/src/f16
  dir/src/f17
  dir/src/f18
  dir/src/f19
  dir/src/f2
  dir/src/f20
  dir/src/f3
  dir/src/f4
  dir/src/f5
  dir/src/f6
  dir/src/f7
  dir/src/f8
  dir/src/f9

  $ cd ..

Testing the --narrowspec flag to clone

  $ cat >> narrowspecs <<EOF
  > %include foo
  > [include]
  > path:dir/tests/
  > path:dir/src/f12
  > EOF

  $ hg clone ssh://user@dummy/master specfile --narrowspec narrowspecs
  reading narrowspec from '$TESTTMP/narrowspecs'
  config error: cannot specify other files using '%include' in narrowspec
  [30]

  $ cat > narrowspecs <<EOF
  > [include]
  > path:dir/tests/
  > path:dir/src/f12
  > EOF

  $ hg clone ssh://user@dummy/master specfile --narrowspec narrowspecs
  reading narrowspec from '$TESTTMP/narrowspecs'
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 40 changesets with 21 changes to 21 files
  new changesets 681085829a73:26ce255d5b5d
  updating to branch default
  21 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd specfile
  $ hg tracked
  I path:dir/src/f12
  I path:dir/tests
  $ cd ..