Buildresult: linus/nds32-defconfig/nds32le-gcc8 built on Jan 24 2019, 08:57

kisskb

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Status:	OK
Date/Time:	Jan 24 2019, 08:57
Duration:	0:00:56.312827
Builder:	ka1
Revision:	Revert "Change mincore() to count "mapped" pages rather than "cached" pages" (`30bac164aca750892b93eef350439a0562a68647)`
Target:	linus/nds32-defconfig/nds32le-gcc8
Branch:	linus
Compiler:	nds32le-gcc8 (nds32le-linux-gcc (GCC) 8.1.0 / GNU ld (GNU Binutils) 2.30.51.20180307)
Config:	defconfig (download)
Log:	Download original No warnings found in log. Full Log # git rev-parse -q --verify 30bac164aca750892b93eef350439a0562a68647^{commit} 30bac164aca750892b93eef350439a0562a68647 already have revision, skipping fetch # git checkout -q -f -B kisskb 30bac164aca750892b93eef350439a0562a68647 # git clean -qxdf # < git log -1 # commit 30bac164aca750892b93eef350439a0562a68647 # Author: Linus Torvalds <torvalds@linux-foundation.org> # Date: Thu Jan 24 09:04:37 2019 +1300 # # Revert "Change mincore() to count "mapped" pages rather than "cached" pages" # # This reverts commit 574823bfab82d9d8fa47f422778043fbb4b4f50e. # # It turns out that my hope that we could just remove the code that # exposes the cache residency status from mincore() was too optimistic. # # There are various random users that want it, and one example would be # the Netflix database cluster maintenance. To quote Josh Snyder: # # "For Netflix, losing accurate information from the mincore syscall # would lengthen database cluster maintenance operations from days to # months. We rely on cross-process mincore to migrate the contents of a # page cache from machine to machine, and across reboots. # # To do this, I wrote and maintain happycache [1], a page cache # dumper/loader tool. It is quite similar in architecture to pgfincore, # except that it is agnostic to workload. The gist of happycache's # operation is "produce a dump of residence status for each page, do # some operation, then reload exactly the same pages which were present # before." happycache is entirely dependent on accurate reporting of the # in-core status of file-backed pages, as accessed by another process. # # We primarily use happycache with Cassandra, which (like Postgres + # pgfincore) relies heavily on OS page cache to reduce disk accesses. # Because our workloads never experience a cold page cache, we are able # to provision hardware for a peak utilization level that is far lower # than the hypothetical "every query is a cache miss" peak. # # A database warmed by happycache can be ready for service in seconds # (bounded only by the performance of the drives and the I/O subsystem), # with no period of in-service degradation. By contrast, putting a # database in service without a page cache entails a potentially # unbounded period of degradation (at Netflix, the time to populate a # single node's cache via natural cache misses varies by workload from # hours to weeks). If a single node upgrade were to take weeks, then # upgrading an entire cluster would take months. Since we want to apply # security upgrades (and other things) on a somewhat tighter schedule, # we would have to develop more complex solutions to provide the same # functionality already provided by mincore. # # At the bottom line, happycache is designed to benignly exploit the # same information leak documented in the paper [2]. I think it makes # perfect sense to remove cross-process mincore functionality from # unprivileged users, but not to remove it entirely" # # We do have an alternate approach that limits the cache residency # reporting only to processes that have write permissions to the file, so # we can fix the original information leak issue that way. It involves # _adding_ code rather than removing it, which is sad, but hey, at least # we haven't found any users that would find the restrictions # unacceptable. # # So revert the optimistic first approach to make room for that alternate # fix instead. # # Reported-by: Josh Snyder <joshs@netflix.com> # Cc: Jiri Kosina <jikos@kernel.org> # Cc: Dominique Martinet <asmadeus@codewreck.org> # Cc: Andy Lutomirski <luto@amacapital.net> # Cc: Dave Chinner <david@fromorbit.com> # Cc: Kevin Easton <kevin@guarana.org> # Cc: Matthew Wilcox <willy@infradead.org> # Cc: Cyril Hrubis <chrubis@suse.cz> # Cc: Vlastimil Babka <vbabka@suse.cz> # Cc: Tejun Heo <tj@kernel.org> # Cc: Kirill A. Shutemov <kirill@shutemov.name> # Cc: Daniel Gruss <daniel@gruss.cc> # Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> # < /opt/cross/kisskb/korg/gcc-8.1.0-nolibc/nds32le-linux/bin/nds32le-linux-gcc --version # < /opt/cross/kisskb/korg/gcc-8.1.0-nolibc/nds32le-linux/bin/nds32le-linux-ld --version # < git log --format=%s --max-count=1 30bac164aca750892b93eef350439a0562a68647 # < make -s -j 48 ARCH=nds32 O=/kisskb/build/linus_nds32-defconfig_nds32le CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/nds32le-linux/bin/nds32le-linux- defconfig # make -s -j 48 ARCH=nds32 O=/kisskb/build/linus_nds32-defconfig_nds32le CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/nds32le-linux/bin/nds32le-linux- Completed OK # rm -rf /kisskb/build/linus_nds32-defconfig_nds32le # Build took: 0:00:56.312827

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