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Yang Shi 98879b3b9e mm: vmscan: correct some vmscan counters for THP swapout 
Commit bd4c82c22c ("mm, THP, swap: delay splitting THP after swapped
out"), THP can be swapped out in a whole.  But, nr_reclaimed and some
other vm counters still get inc'ed by one even though a whole THP (512
pages) gets swapped out.

This doesn't make too much sense to memory reclaim.

For example, direct reclaim may just need reclaim SWAP_CLUSTER_MAX
pages, reclaiming one THP could fulfill it.  But, if nr_reclaimed is not
increased correctly, direct reclaim may just waste time to reclaim more
pages, SWAP_CLUSTER_MAX * 512 pages in worst case.

And, it may cause pgsteal_{kswapd|direct} is greater than
pgscan_{kswapd|direct}, like the below:

pgsteal_kswapd 122933
pgsteal_direct 26600225
pgscan_kswapd 174153
pgscan_direct 14678312

nr_reclaimed and nr_scanned must be fixed in parallel otherwise it would
break some page reclaim logic, e.g.

vmpressure: this looks at the scanned/reclaimed ratio so it won't change
semantics as long as scanned & reclaimed are fixed in parallel.

compaction/reclaim: compaction wants a certain number of physical pages
freed up before going back to compacting.

kswapd priority raising: kswapd raises priority if we scan fewer pages
than the reclaim target (which itself is obviously expressed in order-0
pages).  As a result, kswapd can falsely raise its aggressiveness even
when it's making great progress.

Other than nr_scanned and nr_reclaimed, some other counters, e.g.
pgactivate, nr_skipped, nr_ref_keep and nr_unmap_fail need to be fixed too
since they are user visible via cgroup, /proc/vmstat or trace points,
otherwise they would be underreported.

When isolating pages from LRUs, nr_taken has been accounted in base page,
but nr_scanned and nr_skipped are still accounted in THP.  It doesn't make
too much sense too since this may cause trace point underreport the
numbers as well.

So accounting those counters in base page instead of accounting THP as one
page.

nr_dirty, nr_unqueued_dirty, nr_congested and nr_writeback are used by
file cache, so they are not impacted by THP swap.

This change may result in lower steal/scan ratio in some cases since THP
may get split during page reclaim, then a part of tail pages get reclaimed
instead of the whole 512 pages, but nr_scanned is accounted by 512,
particularly for direct reclaim.  But, this should be not a significant
issue.

Link: http://lkml.kernel.org/r/1559025859-72759-2-git-send-email-yang.shi@linux.alibaba.com
Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
Reviewed-by: "Huang, Ying" <ying.huang@intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Hillf Danton <hdanton@sina.com>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-07-12 11:05:46 -07:00
arch arm64: move jump_label_init() before parse_early_param() 2019-07-12 11:05:46 -07:00
block for-5.3/block-20190708 2019-07-09 10:45:06 -07:00
certs Revert "Merge tag 'keys-acl-20190703' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs" 2019-07-10 18:43:43 -07:00
crypto Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2019-07-08 20:57:08 -07:00
Documentation mm: security: introduce init_on_alloc=1 and init_on_free=1 boot options 2019-07-12 11:05:46 -07:00
drivers mm: security: introduce init_on_alloc=1 and init_on_free=1 boot options 2019-07-12 11:05:46 -07:00
fs memcg, fsnotify: no oom-kill for remote memcg charging 2019-07-12 11:05:43 -07:00
include mm: security: introduce init_on_alloc=1 and init_on_free=1 boot options 2019-07-12 11:05:46 -07:00
init mm: init: report memory auto-initialization features at boot time 2019-07-12 11:05:46 -07:00
ipc treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 441 2019-06-05 17:37:17 +02:00
kernel mm/nvdimm: add is_ioremap_addr and use that to check ioremap address 2019-07-12 11:05:40 -07:00
lib lib/test_kasan: Add test for double-kzfree detection 2019-07-12 11:05:42 -07:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
mm mm: vmscan: correct some vmscan counters for THP swapout 2019-07-12 11:05:46 -07:00
net mm: security: introduce init_on_alloc=1 and init_on_free=1 boot options 2019-07-12 11:05:46 -07:00
samples Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next 2019-07-11 10:55:49 -07:00
scripts scripts/spelling.txt: add more spellings to spelling.txt 2019-07-12 11:05:41 -07:00
security mm: security: introduce init_on_alloc=1 and init_on_free=1 boot options 2019-07-12 11:05:46 -07:00
sound It's been a relatively busy cycle for docs: 2019-07-09 12:34:26 -07:00
tools Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next 2019-07-11 10:55:49 -07:00
usr user/Makefile: Fix typo and capitalization in comment section 2018-12-11 00:18:03 +09:00
virt arm64: switch to generic version of pte allocation 2019-07-12 11:05:45 -07:00
.clang-format Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2019-04-17 11:26:25 -07:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes
.gitignore .gitignore: exclude .get_maintainer.ignore and .gitattributes 2019-05-18 11:49:54 +09:00
.mailmap MAINTAINERS: Update my email address 2019-06-18 14:37:27 +01:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next 2019-06-25 01:32:59 +02:00
Kbuild Kbuild updates for v5.1 2019-03-10 17:48:21 -07:00
Kconfig docs: kbuild: convert docs to ReST and rename to *.rst 2019-06-14 14:21:21 -06:00
MAINTAINERS MAINTAINERS: nilfs2: update email address 2019-07-12 11:05:40 -07:00
Makefile Linux 5.2 2019-07-07 15:41:56 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.