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Re: [PATCH 3/6] strbuf_getwholeline: use getc_unlocked

From
Jeff King <peff@peff.net>
Date
Apr 8, 2015, 00:17 UTC
Message-ID
<20150408001712.GA16798@peff.net>
In-Reply-To
<87k2xn8sqq.fsf@rasmusvillemoes.dk>
On Wed, Apr 08, 2015 at 12:43:09AM +0200, Rasmus Villemoes wrote:
Show 9 quoted lines
> Hm, I'm afraid it's not that simple. It seems that data may be lost from
> the stream if getdelim encounters ENOMEM: Looking at the glibc
> implementation (libio/iogetdelim.c), if reallocating the user buffer
> fails, -1 is returned (presumably with errno==ENOMEM set by realloc), and
> there's no way of knowing how many bytes were already copied to the
> buffer (cur_len).
> 
> For regular files, I suppose one could do a ftell/fseek dance. For
> other cases, I don't see a reliable way to retry upon ENOMEM.
Ah, right, that makes sense.

I think it may be OK to just `die()` on ENOMEM here. The "try to free" routine is basically about unmapping pack memory, in case it is clogging up the address space (it is mmap'd, so it shouldn't cause real RAM pressure; the OS can just drop the pages from the cache if it wants).

But getdelim() calls are not likely to be big allocations in the first place (so they are not likely to fail at all, and if they do, we really are horribly out of memory). I'd also question whether release_pack_memory is doing anything in practice on 64-bit machines. We have quite a bit of address space to work with in that case.

-Peff
Previous: Rasmus VillemoesNext: Jeff King
Message 15 of 44 in “address packed-refs speed regressions”
  1. 0/6 address packed-refs speed regressionsJeff King, Apr 5, 2015
  2. 1/6 strbuf_getwholeline: use getc macroJeff King, Apr 5, 2015
  3. 2/6 git-compat-util: add fallbacks for unlocked stdioJeff King, Apr 5, 2015
  4. 3/6 strbuf_getwholeline: use getc_unlockedJeff King, Apr 5, 2015
  5. Jeff KingApr 5, 2015
  6. Jeff KingApr 5, 2015
  7. Jeff KingApr 5, 2015
  8. Junio C HamanoApr 5, 2015
  9. Duy NguyenApr 5, 2015
  10. Jeff KingApr 5, 2015
  11. Junio C HamanoApr 5, 2015
  12. Rasmus VillemoesApr 7, 2015
  13. Jeff KingApr 7, 2015
  14. Rasmus VillemoesApr 7, 2015
  15. Jeff KingApr 8, 2015
  16. 4/6 strbuf: add an optimized 1-character strbuf_growJeff King, Apr 5, 2015
  17. Eric SunshineApr 6, 2015
  18. Jeff KingApr 6, 2015
  19. 5/6 t1430: add another refs-escape testJeff King, Apr 5, 2015
  20. 6/6 refname_is_safe: avoid expensive normalize_path_copy callJeff King, Apr 5, 2015
  21. René ScharfeApr 5, 2015
  22. Jeff KingApr 5, 2015
  23. Jeff KingApr 5, 2015
  24. René ScharfeApr 5, 2015
  25. René ScharfeApr 5, 2015
  26. Jeff KingApr 6, 2015
  27. 0/9 address packed-refs speed regressionsJeff King, Apr 16, 2015
  28. 1/9 strbuf_getwholeline: use getc macroJeff King, Apr 16, 2015
  29. 2/9 git-compat-util: add fallbacks for unlocked stdioJeff King, Apr 16, 2015
  30. 3/9 strbuf_getwholeline: use getc_unlockedJeff King, Apr 16, 2015
  31. 4/9 config: use getc_unlocked when reading from fileJeff King, Apr 16, 2015
  32. 5/9 strbuf_addch: avoid calling strbuf_growJeff King, Apr 16, 2015
  33. 6/9 strbuf_getwholeline: avoid calling strbuf_growJeff King, Apr 16, 2015
  34. 7/9 strbuf_getwholeline: use getdelim if it is availableJeff King, Apr 16, 2015
  35. Eric SunshineApr 17, 2015
  36. Jeff KingApr 21, 2015
  37. Eric SunshineMay 8, 2015
  38. Jeff KingMay 9, 2015
  39. Eric SunshineJun 2, 2015
  40. Johannes SchindelinApr 22, 2015
  41. Jeff KingApr 22, 2015
  42. 8/9 read_packed_refs: avoid double-checking sane refsJeff King, Apr 16, 2015
  43. 9/9 t1430: add another refs-escape testJeff King, Apr 16, 2015
  44. Jeff KingApr 16, 2015

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