Re: [PATCH v2 16/20] builtin/gc.c: guess the size of the revindex

On Wed, Jan 13, 2021 at 10:33:01PM -0800, Junio C Hamano wrote:

Taylor Blau [off-list ref] writes:

quoted

'estimate_repack_memory()' takes into account the amount of memory
required to load the reverse index in memory by multiplying the assumed
number of objects by the size of the 'revindex_entry' struct.

Prepare for hiding the definition of 'struct revindex_entry' by removing
a 'sizeof()' of that type from outside of pack-revindex.c. Instead,
guess that one off_t and one uint32_t are required per object. Strictly
speaking, this is a worse guess than asking for 'sizeof(struct
revindex_entry)' directly, since the true size of this struct is 16
bytes with padding on the end of the struct in order to align the offset
field.

Meaning that we under-estimate by 25%?

In this area, yes. I'm skeptical that this estimate is all that
important, since it doesn't seem to take into account the memory
required to select delta/base candidates [1].

Thanks,
Taylor

[1]: https://lore.kernel.org/git/X%2F1roycRbYPjnI3l@coredump.intra.peff.net/ (local)