# git rev-parse -q --verify 981ee95cc1f5905ae4936b0dd501085909cdc14f^{commit} # git fetch -q -n -f git://fs.ozlabs.ibm.com/kernel/linus master # git rev-parse -q --verify 981ee95cc1f5905ae4936b0dd501085909cdc14f^{commit} 981ee95cc1f5905ae4936b0dd501085909cdc14f # git checkout -q -f -B kisskb 981ee95cc1f5905ae4936b0dd501085909cdc14f # git clean -qxdf # < git log -1 # commit 981ee95cc1f5905ae4936b0dd501085909cdc14f # Author: Mateusz Guzik # Date: Wed Jan 25 16:55:57 2023 +0100 # # vfs: avoid duplicating creds in faccessat if possible # # access(2) remains commonly used, for example on exec: # access("/etc/ld.so.preload", R_OK) # # or when running gcc: strace -c gcc empty.c # # % time seconds usecs/call calls errors syscall # ------ ----------- ----------- --------- --------- ---------------- # 0.00 0.000000 0 42 26 access # # It falls down to do_faccessat without the AT_EACCESS flag, which in turn # results in allocation of new creds in order to modify fsuid/fsgid and # caps. This is a very expensive process single-threaded and most notably # multi-threaded, with numerous structures getting refed and unrefed on # imminent new cred destruction. # # Turns out for typical consumers the resulting creds would be identical # and this can be checked upfront, avoiding the hard work. # # An access benchmark plugged into will-it-scale running on Cascade Lake # shows: # # test proc before after # access1 1 1310582 2908735 (+121%) # distinct files # access1 24 4716491 63822173 (+1353%) # distinct files # access2 24 2378041 5370335 (+125%) # same file # # The above benchmarks are not integrated into will-it-scale, but can be # found in a pull request: # # https://github.com/antonblanchard/will-it-scale/pull/36/files # # Signed-off-by: Mateusz Guzik # Cc: Al Viro # Signed-off-by: Linus Torvalds # < /opt/cross/kisskb/korg/gcc-8.5.0-nolibc/x86_64-linux/bin/x86_64-linux-gcc --version # < /opt/cross/kisskb/korg/gcc-8.5.0-nolibc/x86_64-linux/bin/x86_64-linux-ld --version # < git log --format=%s --max-count=1 981ee95cc1f5905ae4936b0dd501085909cdc14f # < make -s -j 24 ARCH=x86 O=/kisskb/build/linus_x86_64_defconfig_x86_64-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.5.0-nolibc/x86_64-linux/bin/x86_64-linux- x86_64_defconfig # < make -s -j 24 ARCH=x86 O=/kisskb/build/linus_x86_64_defconfig_x86_64-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.5.0-nolibc/x86_64-linux/bin/x86_64-linux- help # make -s -j 24 ARCH=x86 O=/kisskb/build/linus_x86_64_defconfig_x86_64-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.5.0-nolibc/x86_64-linux/bin/x86_64-linux- olddefconfig # make -s -j 24 ARCH=x86 O=/kisskb/build/linus_x86_64_defconfig_x86_64-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.5.0-nolibc/x86_64-linux/bin/x86_64-linux- Completed OK # rm -rf /kisskb/build/linus_x86_64_defconfig_x86_64-gcc8 # Build took: 0:04:31.037752