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As reported in [1] the code I added in94da9193a6("grep: add support for PCRE v2", 2017-06-01) to use a custom JIT stack has never worked. It was incorrectly copy/pasted from code I added infbaceaac47("grep: add support for the PCRE v1 JIT API", 2017-05-25), which did work. Thus our intention of starting with 1 byte of stack at a maximum of 1 MB didn't happen, we'd always use the 32 KB stack provided by PCRE v2's jit_machine_stack_exec()[2]. The reason I allocated a custom stack at all was this advice in pcrejit(3) (same in pcre2jit(3)): "By default, it uses 32KiB on the machine stack. However, some large or complicated patterns need more than this" Since we've haven't had any reports of users running into PCRE2_ERROR_JIT_STACKLIMIT in the wild I think we can safely assume that we can just use the library defaults instead and drop this code. This won't change with the wider use of PCRE v2 in ed0479ce3d ("Merge branch 'ab/no-kwset' into next", 2019-07-15), a fixed string search is not a "large or complicated pattern". For good measure I ran the performance test noted in94da9193a6, although the command is simpler now due to my0f50c8e32c("Makefile: remove the NO_R_TO_GCC_LINKER flag", 2019-05-17): GIT_PERF_REPEAT_COUNT=30 GIT_PERF_LARGE_REPO=~/g/linux GIT_PERF_MAKE_OPTS='-j8 USE_LIBPCRE2=Y CFLAGS=-O3 LIBPCREDIR=/home/avar/g/pcre2/inst' ./run HEAD~ HEAD p7820-grep-engines.sh Just the /perl/ results are: Test HEAD~ HEAD --------------------------------------------------------------------------------------- 7820.3: perl grep 'how.to' 0.17(0.27+0.65) 0.17(0.24+0.68) +0.0% 7820.7: perl grep '^how to' 0.16(0.23+0.66) 0.16(0.23+0.67) +0.0% 7820.11: perl grep '[how] to' 0.18(0.35+0.62) 0.18(0.33+0.65) +0.0% 7820.15: perl grep '(e.t[^ ]*|v.ry) rare' 0.17(0.45+0.54) 0.17(0.49+0.50) +0.0% 7820.19: perl grep 'm(ú|u)lt.b(æ|y)te' 0.16(0.33+0.58) 0.16(0.29+0.62) +0.0% So, as expected there's no change, and running with valgrind reveals that we have fewer allocations now. As noted in [3] there are known regexes that will fail with the lower stack limit, the way GNU grep fixed it is interesting, although I believe the implementation is overly verbose, they could make PCRE v2 handle that gradual re-allocation, that's what min/max memory is for. So we might end up bringing this back, I'm more inclined to just kick such cases upstairs to PCRE maintainers as a bug, perhaps they'll add some overall "just allocate more then" flag to make this easier. In any case there's no functional change here, we didn't have a custom stack, so let's apply this first, we can always revert it later. 1. https://public-inbox.org/git/20190721194052.15440-1-carenas@gmail.com/ 2. I didn't really intend to start with 1 byte, looking at the PCRE v2 code again what happened is that I cargo-culted some of PCRE v2's own test code which was meant to test re-allocations. It's more sane to start with say 32 KB with a max of 1 MB, as pcre2grep.c does. 3. https://public-inbox.org/git/CAPUEspjj+fG8QDmf=bZXktfpLgkgiu34HTjKLhm-cmEE04FE-A@mail.gmail.com/ Reported-by: Carlo Marcelo Arenas Belón <carenas@gmail.com> Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Git - fast, scalable, distributed revision control system
Git is a fast, scalable, distributed revision control system with an unusually rich command set that provides both high-level operations and full access to internals.
Git is an Open Source project covered by the GNU General Public License version 2 (some parts of it are under different licenses, compatible with the GPLv2). It was originally written by Linus Torvalds with help of a group of hackers around the net.
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- stupid. contemptible and despicable. simple. Take your pick from the dictionary of slang.
- "global information tracker": you're in a good mood, and it actually works for you. Angels sing, and a light suddenly fills the room.
- "goddamn idiotic truckload of sh*t": when it breaks