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From: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
To: git@vger.kernel.org
Cc: "Junio C Hamano" <gitster@pobox.com>,
	"Carlo Marcelo Arenas Belón" <carenas@gmail.com>,
	"Beat Bolli" <dev+git@drbeat.li>,
	"Johannes Schindelin" <Johannes.Schindelin@gmx.de>,
	"Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
Subject: [PATCH v2 2/8] grep: stop "using" a custom JIT stack with PCRE v2
Date: Fri, 26 Jul 2019 17:08:12 +0200	[thread overview]
Message-ID: <20190726150818.6373-3-avarab@gmail.com> (raw)
In-Reply-To: <20190724151415.3698-1-avarab@gmail.com>

As reported in [1] the code I added in 94da9193a6 ("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 in
fbaceaac47 ("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 in 94da9193a6,
although the command is simpler now due to my 0f50c8e32c ("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>
---
 grep.c | 10 ----------
 grep.h |  4 ----
 2 files changed, 14 deletions(-)

diff --git a/grep.c b/grep.c
index 95af88cb74..4b1e917ac5 100644
--- a/grep.c
+++ b/grep.c
@@ -534,14 +534,6 @@ static void compile_pcre2_pattern(struct grep_pat *p, const struct grep_opt *opt
 			p->pcre2_jit_on = 0;
 			return;
 		}
-
-		p->pcre2_jit_stack = pcre2_jit_stack_create(1, 1024 * 1024, NULL);
-		if (!p->pcre2_jit_stack)
-			die("Couldn't allocate PCRE2 JIT stack");
-		p->pcre2_match_context = pcre2_match_context_create(NULL);
-		if (!p->pcre2_match_context)
-			die("Couldn't allocate PCRE2 match context");
-		pcre2_jit_stack_assign(p->pcre2_match_context, NULL, p->pcre2_jit_stack);
 	}
 }
 
@@ -585,8 +577,6 @@ static void free_pcre2_pattern(struct grep_pat *p)
 	pcre2_compile_context_free(p->pcre2_compile_context);
 	pcre2_code_free(p->pcre2_pattern);
 	pcre2_match_data_free(p->pcre2_match_data);
-	pcre2_jit_stack_free(p->pcre2_jit_stack);
-	pcre2_match_context_free(p->pcre2_match_context);
 }
 #else /* !USE_LIBPCRE2 */
 static void compile_pcre2_pattern(struct grep_pat *p, const struct grep_opt *opt)
diff --git a/grep.h b/grep.h
index d35a137fcb..4d8e300175 100644
--- a/grep.h
+++ b/grep.h
@@ -29,8 +29,6 @@ typedef int pcre_jit_stack;
 typedef int pcre2_code;
 typedef int pcre2_match_data;
 typedef int pcre2_compile_context;
-typedef int pcre2_match_context;
-typedef int pcre2_jit_stack;
 #endif
 #include "thread-utils.h"
 #include "userdiff.h"
@@ -93,8 +91,6 @@ struct grep_pat {
 	pcre2_code *pcre2_pattern;
 	pcre2_match_data *pcre2_match_data;
 	pcre2_compile_context *pcre2_compile_context;
-	pcre2_match_context *pcre2_match_context;
-	pcre2_jit_stack *pcre2_jit_stack;
 	uint32_t pcre2_jit_on;
 	unsigned fixed:1;
 	unsigned ignore_case:1;
-- 
2.22.0.455.g172b71a6c5


  parent reply	other threads:[~2019-07-26 15:09 UTC|newest]

Thread overview: 70+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-21 19:40 [PATCH] grep: use custom JIT stack with pcre2 Carlo Marcelo Arenas Belón
2019-07-24 15:14 ` [PATCH 0/3] grep: PCRE JIT fixes Ævar Arnfjörð Bjarmason
2019-07-24 16:18   ` Junio C Hamano
2019-07-24 20:03     ` Ævar Arnfjörð Bjarmason
2019-07-26 15:08   ` [PATCH v2 0/8] grep: PCRE JIT fixes + ab/no-kwset fix Ævar Arnfjörð Bjarmason
2019-07-26 20:27     ` Junio C Hamano
2019-07-29  9:20       ` Ævar Arnfjörð Bjarmason
2019-07-29 16:12         ` Junio C Hamano
2019-07-26 15:08   ` [PATCH v2 1/8] grep: remove overly paranoid BUG(...) code Ævar Arnfjörð Bjarmason
2019-07-26 15:08   ` Ævar Arnfjörð Bjarmason [this message]
2019-07-29  0:33     ` [PATCH v2 2/8] grep: stop "using" a custom JIT stack with PCRE v2 Carlo Arenas
2019-07-26 15:08   ` [PATCH v2 3/8] grep: stop using a custom JIT stack with PCRE v1 Ævar Arnfjörð Bjarmason
2019-07-29  1:26     ` Carlo Arenas
2019-07-26 15:08   ` [PATCH v2 4/8] grep: consistently use "p->fixed" in compile_regexp() Ævar Arnfjörð Bjarmason
2019-07-29  1:48     ` Carlo Arenas
2019-07-29  9:05       ` Ævar Arnfjörð Bjarmason
2019-07-29  9:13         ` Ævar Arnfjörð Bjarmason
2019-07-29 16:23           ` Junio C Hamano
2019-07-26 15:08   ` [PATCH v2 5/8] grep: create a "is_fixed" member in "grep_pat" Ævar Arnfjörð Bjarmason
2019-07-26 15:08   ` [PATCH v2 6/8] grep: stess test PCRE v2 on invalid UTF-8 data Ævar Arnfjörð Bjarmason
2019-07-26 20:34     ` Junio C Hamano
2019-07-26 21:55       ` Ævar Arnfjörð Bjarmason
2019-07-29  3:06     ` Carlo Arenas
2019-11-26 21:50     ` [PATCH] t7812: add missing redirects Andreas Schwab
2019-11-26 22:27       ` Johannes Schindelin
2019-11-26 23:11         ` Andreas Schwab
2019-11-27 11:58           ` Jeff King
2019-11-30  0:46       ` [PATCH] t7812: expect failure for grep -i with invalid UTF-8 data Todd Zullinger
2019-11-30  8:00         ` Andreas Schwab
2019-12-01 16:33           ` Junio C Hamano
2019-12-01 17:09             ` Andreas Schwab
2019-12-01 18:32             ` Todd Zullinger
2019-12-02  6:13               ` Junio C Hamano
2019-07-26 15:08   ` [PATCH v2 7/8] grep: do not enter PCRE2_UTF mode on fixed matching Ævar Arnfjörð Bjarmason
2019-07-26 20:36     ` Junio C Hamano
2019-07-26 15:08   ` [PATCH v2 8/8] grep: optimistically use PCRE2_MATCH_INVALID_UTF Ævar Arnfjörð Bjarmason
2019-07-26 21:07     ` Junio C Hamano
2019-07-26 21:53       ` Ævar Arnfjörð Bjarmason
2019-07-26 21:57         ` Ævar Arnfjörð Bjarmason
2021-01-24  2:12     ` [PATCH v3 0/4] grep: better support invalid UTF-8 haystacks Ævar Arnfjörð Bjarmason
2021-01-24 11:48       ` [PATCH v4 0/2] " Ævar Arnfjörð Bjarmason
2021-01-24 17:28         ` [PATCH v5 " Ævar Arnfjörð Bjarmason
2021-01-24 17:28         ` [PATCH v5 1/2] grep/pcre2 tests: don't rely on invalid UTF-8 data test Ævar Arnfjörð Bjarmason
2021-01-24 17:28         ` [PATCH v5 2/2] grep/pcre2: better support invalid UTF-8 haystacks Ævar Arnfjörð Bjarmason
2021-01-24 11:48       ` [PATCH v4 1/2] grep/pcre2 tests: don't rely on invalid UTF-8 data test Ævar Arnfjörð Bjarmason
2021-01-24 11:48       ` [PATCH v4 2/2] grep/pcre2: better support invalid UTF-8 haystacks Ævar Arnfjörð Bjarmason
2021-01-24 13:53         ` Ramsay Jones
2021-01-24 14:24           ` Ramsay Jones
2021-01-24 14:49             ` Ævar Arnfjörð Bjarmason
2021-01-24 16:10               ` Ramsay Jones
2021-01-24 17:29                 ` Ævar Arnfjörð Bjarmason
2021-01-24  2:12     ` [PATCH v3 1/4] grep/pcre2 tests: don't rely on invalid UTF-8 data test Ævar Arnfjörð Bjarmason
2021-01-24  2:12     ` [PATCH v3 2/4] grep/pcre2: simplify boolean spaghetti Ævar Arnfjörð Bjarmason
2021-01-24  5:33       ` Junio C Hamano
2021-01-24 10:45         ` Johannes Sixt
2021-01-24  2:12     ` [PATCH v3 3/4] grep/pcre2: further " Ævar Arnfjörð Bjarmason
2021-01-24  2:12     ` [PATCH v3 4/4] grep/pcre2: better support invalid UTF-8 haystacks Ævar Arnfjörð Bjarmason
2019-07-24 15:14 ` [PATCH 1/3] grep: remove overly paranoid BUG(...) code Ævar Arnfjörð Bjarmason
2019-07-24 15:14 ` [PATCH 2/3] grep: stop "using" a custom JIT stack with PCRE v2 Ævar Arnfjörð Bjarmason
2019-07-24 16:24   ` Junio C Hamano
2019-07-24 20:06     ` Ævar Arnfjörð Bjarmason
2019-07-25  5:11       ` Carlo Arenas
2019-07-24 15:14 ` [PATCH 3/3] grep: stop using a custom JIT stack with PCRE v1 Ævar Arnfjörð Bjarmason
2019-07-26 13:15   ` Carlo Arenas
2019-07-26 13:50     ` Ævar Arnfjörð Bjarmason
2019-07-26 14:12       ` Carlo Arenas
2019-07-26 14:43         ` Ævar Arnfjörð Bjarmason
2019-07-26 20:26           ` [RFC PATCH 0/2] PCRE1 cleanup Carlo Marcelo Arenas Belón
2019-07-26 20:26             ` [RFC PATCH 1/2] grep: make sure NO_LIBPCRE1_JIT disable JIT in PCRE1 Carlo Marcelo Arenas Belón
2019-07-26 20:26             ` [RFC PATCH 2/2] grep: refactor and simplify PCRE1 support Carlo Marcelo Arenas Belón

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