On 2022-06-28 at 18:30:20, Taylor Blau wrote: > The size and padding of `struct object_entry` is an important factor in > determining the memory usage of `pack-objects`. For this reason, > 3b13a5f263 (pack-objects: reorder members to shrink struct object_entry, > 2018-04-14) added a comment containing some information from pahole > indicating the size and padding of that struct. > > Unfortunately, this comment hasn't been updated since 9ac3f0e5b3 > (pack-objects: fix performance issues on packing large deltas, > 2018-07-22), despite the size of this struct changing many times since > that commit. > > To see just how often the size of object_entry changes, I skimmed the > first-parent history with this script: > > for sha in $(git rev-list --first-parent --reverse 9ac3f0e..) > do > echo -n "$sha " > git checkout -q $sha > make -s pack-objects.o 2>/dev/null > pahole -C object_entry pack-objects.o | sed -n \ > -e 's/\/\* size: \([0-9]*\).*/size \1/p' \ > -e 's/\/\*.*padding: \([0-9]*\).*/padding \1/p' | xargs > done | uniq -f1 > > In between each merge, the size of object_entry changes too often to > record every instance here. But the important merges (along with their > corresponding sizes and bit paddings) in chronological order are: > > ad635e82d6 (Merge branch 'nd/pack-objects-pack-struct', 2018-05-23) size 80 padding 4 > 29d9e3e2c4 (Merge branch 'nd/pack-deltify-regression-fix', 2018-08-22) size 80 padding 9 > 3ebdef2e1b (Merge branch 'jk/pack-delta-reuse-with-bitmap', 2018-09-17) size 80 padding 8 > 33e4ae9c50 (Merge branch 'bc/sha-256', 2019-01-29) size 96 padding 8 > > (indicating that the current size of the struct is 96 bytes, with 8 > padding bits). > > Even though this comment was written in a good spirit, it is updated > infrequently enough that is serves to confuse rather than to encourage I think you wanted to say, "that it serves:. > contributors to update the appropriate values when the modify the > definition of object_entry. > > For that reason, eliminate the confusion by removing the comment > altogether. > > Signed-off-by: Taylor Blau <me@xxxxxxxxxxxx> I agree with your rationale and that we should remove this. -- brian m. carlson (he/him or they/them) Toronto, Ontario, CA
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