On Sat, Mar 17, 2018 at 11:05 PM, Ævar Arnfjörð Bjarmason <avarab@xxxxxxxxx> wrote: > > On Wed, Feb 28 2018, Duy Nguyen jotted: > >> linux-2.6.git current has 6483999 objects. "git gc" on my poor laptop >> consumes 1.7G out of 4G RAM, pushing lots of data to swap and making >> all apps nearly unusuable (granted the problem is partly Linux I/O >> scheduler too). So I wonder if we can reduce pack-objects memory >> footprint a bit. >> >> This demonstration patch (probably breaks some tests) would reduce the >> size of struct object_entry from from 136 down to 112 bytes on >> x86-64. There are 6483999 of these objects, so the saving is 17% or >> 148 MB. > > Splitting this off into its own thread. Aside from the improvements in > your repack memory reduction (20180317141033.21545-1-pclouds@xxxxxxxxx) > and gc config (20180316192745.19557-1-pclouds@xxxxxxxxx) series's I'm > wondering why repack takes so much memory to incrementally repack new > stuff when you leave out the base pack. > > Repacking git.git takes around 290MB of memory on my system, but I'd > think that this would make it take a mere few megabytes, since all I'm > asking it to do is pack up the few loose objects that got added and keep > the base pack: > > ... > I left some clue in the new estimate_repack_memory() function in my gc series that could help you find this out. I haven't really tested this case but my guess is the two cache pools we have will likely be filled up close to full anyway and hit delta_base_cache_limit and max_delta_cache_size limits. When these are really full on default configuration, they'll take roughly ~300mb. The second is, I think we still go through all objects to mark which one is included in the new pack, which one not (and probably which one can be delta base candidates). Try calling alloc_report() function at the end of repack to see exactly how much memory is locked in there. This we could perhaps improve for incremental repack by avoiding running rev-list. -- Duy
