view tests/test-amend-subrepo.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)

#testcases obsstore-off obsstore-on

  $ cat << EOF >> $HGRCPATH
  > [extensions]
  > amend =
  > EOF

#if obsstore-on
  $ cat << EOF >> $HGRCPATH
  > [experimental]
  > evolution.createmarkers = True
  > EOF
#endif

Prepare parent repo
-------------------

  $ hg init r
  $ cd r

  $ echo a > a
  $ hg ci -Am0
  adding a

Link first subrepo
------------------

  $ echo 's = s' >> .hgsub
  $ hg add .hgsub
  $ hg init s

amend without .hgsub

  $ hg amend s
  abort: can't commit subrepos without .hgsub
  [255]

amend with subrepo

  $ hg amend
  saved backup bundle to * (glob) (obsstore-off !)
  $ hg status --change .
  A .hgsub
  A .hgsubstate
  A a
  $ cat .hgsubstate
  0000000000000000000000000000000000000000 s

Update subrepo
--------------

add new commit to be amended

  $ echo a >> a
  $ hg ci -m1

amend with dirty subrepo

  $ echo a >> s/a
  $ hg add -R s
  adding s/a
  $ hg amend
  abort: uncommitted changes in subrepository "s"
  (use --subrepos for recursive commit)
  [255]

amend with modified subrepo

  $ hg ci -R s -m0
  $ hg amend
  saved backup bundle to * (glob) (obsstore-off !)
  $ hg status --change .
  M .hgsubstate
  M a
  $ cat .hgsubstate
  f7b1eb17ad24730a1651fccd46c43826d1bbc2ac s

revert subrepo change

  $ hg up -R s -q null
  $ hg amend
  saved backup bundle to * (glob) (obsstore-off !)
  $ hg status --change .
  M a

Link another subrepo
--------------------

add new commit to be amended

  $ echo b >> b
  $ hg ci -qAm2

also checks if non-subrepo change is included

  $ echo a >> a

amend with another subrepo

  $ hg init t
  $ echo b >> t/b
  $ hg ci -R t -Am0
  adding b
  $ echo 't = t' >> .hgsub
  $ hg amend
  saved backup bundle to * (glob) (obsstore-off !)
  $ hg status --change .
  M .hgsub
  M .hgsubstate
  M a
  A b
  $ cat .hgsubstate
  0000000000000000000000000000000000000000 s
  bfb1a4fb358498a9533dabf4f2043d94162f1fcd t

Unlink one subrepo
------------------

add new commit to be amended

  $ echo a >> a
  $ hg ci -m3

  $ echo 't = t' > .hgsub

--interactive won't silently ignore dirty subrepos

  $ echo modified > t/b
  $ hg amend --interactive --config ui.interactive=True
  abort: uncommitted changes in subrepository "t"
  [255]
  $ hg amend --interactive --config ui.interactive=True --config ui.commitsubrepos=True
  abort: uncommitted changes in subrepository "t"
  [255]

  $ hg -R t revert -q --all --no-backup

amend with one subrepo dropped

  $ hg amend
  saved backup bundle to * (glob) (obsstore-off !)
  $ hg status --change .
  M .hgsub
  M .hgsubstate
  M a
  $ cat .hgsubstate
  bfb1a4fb358498a9533dabf4f2043d94162f1fcd t

Unlink subrepos completely
--------------------------

add new commit to be amended

  $ echo a >> a
  $ hg ci -m3

amend with .hgsub removed

  $ hg rm .hgsub
  $ hg amend
  saved backup bundle to * (glob) (obsstore-off !)
  $ hg status --change .
  M a
  R .hgsub
  R .hgsubstate

broken repositories will refuse to push

#if obsstore-off
  $ hg up -q -C 2
#else
  $ hg up -q -C 6
#endif
  $ echo c >> t/b
  $ hg amend -q -R t

  $ hg init ../dest
  $ hg init ../dest/t
  $ hg init ../dest/s
  $ hg push -q ../dest
  abort: subrepo 't' is hidden in revision 04aa62396ec6 (obsstore-on !)
  abort: subrepo 't' not found in revision 04aa62396ec6 (obsstore-off !)
  [255]

... unless forced

  $ hg push --force -q ../dest
  $ hg verify -R ../dest
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  checking dirstate
  checked 5 changesets with 12 changes to 4 files
  checking subrepo links
  subrepo 't' not found in revision 04aa62396ec6
  subrepo 't' not found in revision 6bce99600681

  $ cd ..