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Re: [PATCH 4/6] packed_ref_iterator_begin(): make optimization more general

From
Jeff King <peff@peff.net>
Date
Jan 24, 2018, 20:32 UTC
Message-ID
<20180124203258.GB7773@sigill.intra.peff.net>
In-Reply-To
<bf6c0c67430b936738f5e8891b82022d0127acb0.1516791909.git.mhagger@alum.mit.edu>
On Wed, Jan 24, 2018 at 12:14:14PM +0100, Michael Haggerty wrote:
Show 7 quoted lines
> We can return an empty iterator not only if the `packed-refs` file is
> missing, but also if it is empty or if there are no references whose
> names succeed `prefix`. Optimize away those cases as well by moving
> the call to `find_reference_location()` higher in the function and
> checking whether the determined start position is the same as
> `snapshot->eof`. (This is possible now because the previous commit
> made `find_reference_location()` robust against empty snapshots.)
Makes sense.
Show 9 quoted lines
> @@ -937,11 +942,6 @@ static struct ref_iterator *packed_ref_iterator_begin(
>  	iter->snapshot = snapshot;
>  	acquire_snapshot(snapshot);
>  
> -	if (prefix && *prefix)
> -		start = find_reference_location(snapshot, prefix, 0);
> -	else
> -		start = snapshot->start;
> -

I did a double-take here that we are now looking at the snapshot without calling acquire_snapshot(). But that function is just about taking a refcount on it. The actual acquisition of data happens in get_snapshot().

-Peff
Previous: Michael HaggertyNext: Michael Haggerty
Message 31 of 33 in “packed_ref_cache: don't use mmap() for small files”
  1. packed_ref_cache: don't use mmap() for small filesKim Gybels, Jan 13, 2018
  2. Johannes SchindelinJan 13, 2018
  3. packed_ref_cache: don't use mmap() for small filesKim Gybels, Jan 14, 2018
  4. 0/3 Supplements to "packed_ref_cache: don't use mmap() for small files"Michael Haggerty, Jan 15, 2018
  5. Johannes SchindelinJan 17, 2018
  6. Junio C HamanoJan 17, 2018
  7. 1/3 SQUASH? Mention that `snapshot::buf` can be NULL for empty filesMichael Haggerty, Jan 15, 2018
  8. 2/3 create_snapshot(): exit early if the file was emptyMichael Haggerty, Jan 15, 2018
  9. 3/3 find_reference_location(): don't invoke if `snapshot->buf` is NULLMichael Haggerty, Jan 15, 2018
  10. Jeff KingJan 15, 2018
  11. Kim GybelsJan 15, 2018
  12. Jeff KingJan 15, 2018
  13. packed_ref_cache: don't use mmap() for small filesKim Gybels, Jan 16, 2018
  14. Jeff KingJan 17, 2018
  15. Michael HaggertyJan 21, 2018
  16. Junio C HamanoJan 22, 2018
  17. Michael HaggertyJan 24, 2018
  18. 0/6 Yet another approach to handling empty snapshotsMichael Haggerty, Jan 24, 2018
  19. Jeff KingJan 24, 2018
  20. Junio C HamanoJan 24, 2018
  21. Johannes SchindelinFeb 15, 2018
  22. 1/6 struct snapshot: store `start` rather than `header_len`Michael Haggerty, Jan 24, 2018
  23. Jeff KingJan 24, 2018
  24. 3/6 find_reference_location(): make function safe for empty snapshotsMichael Haggerty, Jan 24, 2018
  25. Jeff KingJan 24, 2018
  26. Junio C HamanoJan 24, 2018
  27. Jeff KingJan 24, 2018
  28. 2/6 create_snapshot(): use `xmemdupz()` rather than a strbufMichael Haggerty, Jan 24, 2018
  29. 5/6 load_contents(): don't try to mmap an empty fileMichael Haggerty, Jan 24, 2018
  30. 4/6 packed_ref_iterator_begin(): make optimization more generalMichael Haggerty, Jan 24, 2018
  31. Jeff KingJan 24, 2018
  32. 6/6 packed_ref_cache: don't use mmap() for small filesMichael Haggerty, Jan 24, 2018
  33. Junio C HamanoJan 24, 2018

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