On 07/11, Jonathan Nieder wrote:
> Hi,
>
> Brandon Williams wrote:
>
> > Convert grep to use 'struct repository' which enables recursing into
> > submodules to be handled in-process.
>
> \o/
>
> This will be even nicer with the changes described at
> https://public-inbox.org/git/20170706202739.6056-1-sbel...@google.com/.
> Until then, I fear it will cause a regression --- see (*) below.
>
> [...]
> > Documentation/git-grep.txt | 7 -
> > builtin/grep.c | 390
> > +++++++++------------------------------------
> > cache.h | 1 -
> > git.c | 2 +-
> > grep.c | 13 --
> > grep.h | 1 -
> > setup.c | 12 +-
> > 7 files changed, 81 insertions(+), 345 deletions(-)
>
> Yay, tests still pass.
>
> [..]
> > --- a/Documentation/git-grep.txt
> > +++ b/Documentation/git-grep.txt
> > @@ -95,13 +95,6 @@ OPTIONS
> > <tree> option the prefix of all submodule output will be the name of
> > the parent project's <tree> object.
> >
> > ---parent-basename <basename>::
> > - For internal use only. In order to produce uniform output with the
> > - --recurse-submodules option, this option can be used to provide the
> > - basename of a parent's <tree> object to a submodule so the submodule
> > - can prefix its output with the parent's name rather than the SHA1 of
> > - the submodule.
>
> Being able to get rid of this is a very nice change.
>
> [...]
> > +++ b/builtin/grep.c
> [...]
> > @@ -366,14 +349,10 @@ static int grep_file(struct grep_opt *opt, const char
> > *filename)
> > {
> > struct strbuf buf = STRBUF_INIT;
> >
> > - if (super_prefix)
> > - strbuf_addstr(&buf, super_prefix);
> > - strbuf_addstr(&buf, filename);
> > -
> > if (opt->relative && opt->prefix_length) {
> > - char *name = strbuf_detach(&buf, NULL);
> > - quote_path_relative(name, opt->prefix, &buf);
> > - free(name);
> > + quote_path_relative(filename, opt->prefix, &buf);
> > + } else {
> > + strbuf_addstr(&buf, filename);
> > }
>
> style micronit: can avoid these braces since both branches are
> single-line.
Didn't realize that with all the deleted lines, I'll fix for the next
version.
>
> [...]
> > @@ -421,284 +400,80 @@ static void run_pager(struct grep_opt *opt, const
> > char *prefix)
> > exit(status);
> > }
> >
> > -static void compile_submodule_options(const struct grep_opt *opt,
> > - const char **argv,
> > - int cached, int untracked,
> > - int opt_exclude, int use_index,
> > - int pattern_type_arg)
> > -{
> [...]
> > - /*
> > - * Limit number of threads for child process to use.
> > - * This is to prevent potential fork-bomb behavior of git-grep as each
> > - * submodule process has its own thread pool.
> > - */
> > - argv_array_pushf(&submodule_options, "--threads=%d",
> > - (num_threads + 1) / 2);
>
> Being able to get rid of this is another very nice change.
>
> [...]
> > + /* add objects to alternates */
> > + add_to_alternates_memory(submodule.objectdir);
>
> (*) This sets up a single in-memory object store with all the
> processed submodules. Processed objects are never freed.
> This means that if I run a command like
>
> git grep --recurse-submodules -e neverfound HEAD
>
> in a project with many submodules then memory consumption scales in
> the same way as if the project were all one repository. By contrast,
> without this patch, git is able to take advantage of the implicit
> free() when each child exits to limit its memory usage.
>
> Worse, this increases the number of pack files git has to pay
> attention to the sum of the numbers of pack files in all the
> repositories processed so far. A single object lookup can take
> O(number of packs * log(number of objects in each pack)) time. That
> means performance is likely to suffer as the number of submodules
> increases (n^2 performance) even on systems with a lot of memory.
>
> Once the object store is part of the repository struct and freeable,
> those problems go away and this patch becomes a no-brainer.
>
> What should happen until then? Should this go in "next" so we can get
> experience with it but with care not to let it graduate to "master"?
I agree that this is an issue and that we need to address by having
an object store per repository. While that is being worked on (by
Stefan) I don't know how long it would take to have it be a reality.
So the question ends up being do we care more about the state of the
code and cleaning up a lot of 'hacks' that I introduced to get grep
working with submodules, or do we care about the performance more. I
don't know which is the right answer but I'd personally like to see the
hacks I added to be removed sooner rather than later. That and I think
that with the code in this sate it would make it easier to transition
once we have per-repository object-stores.
Either way I should add a NEEDSWORK comment here to indicate that it
should be removed once per-repo object-stores exist.
>
> Aside from those two concerns, this patch looks very good from a quick
> skim, though I haven't reviewed it closely line-by-line. Once we know
> how to go forward, I'm happy to look at it again.
>
> Thanks,
> Jonathan
--
Brandon Williams
