6d7942377c
commit f1782c9bc547754f4bd3043fe8cfda53db85f13f upstream.
I received a report about suspicious growth of unreclaimable slabs on
some machines. I've found that it happens on machines with low memory
pressure, and these unreclaimable slabs are external names attached to
dentries.
External names are allocated using generic kmalloc() function, so they
are accounted as unreclaimable. But they are held by dentries, which
are reclaimable, and they will be reclaimed under the memory pressure.
In particular, this breaks MemAvailable calculation, as it doesn't take
unreclaimable slabs into account. This leads to a silly situation, when
a machine is almost idle, has no memory pressure and therefore has a big
dentry cache. And the resulting MemAvailable is too low to start a new
workload.
To address the issue, the NR_INDIRECTLY_RECLAIMABLE_BYTES counter is
used to track the amount of memory, consumed by external names. The
counter is increased in the dentry allocation path, if an external name
structure is allocated; and it's decreased in the dentry freeing path.
To reproduce the problem I've used the following Python script:
import os
for iter in range (0, 10000000):
try:
name = ("/some_long_name_%d" % iter) + "_" * 220
os.stat(name)
except Exception:
pass
Without this patch:
$ cat /proc/meminfo | grep MemAvailable
MemAvailable: 7811688 kB
$ python indirect.py
$ cat /proc/meminfo | grep MemAvailable
MemAvailable: 2753052 kB
With the patch:
$ cat /proc/meminfo | grep MemAvailable
MemAvailable: 7809516 kB
$ python indirect.py
$ cat /proc/meminfo | grep MemAvailable
MemAvailable: 7749144 kB
[guro@fb.com: fix indirectly reclaimable memory accounting for CONFIG_SLOB]
Link: http://lkml.kernel.org/r/20180312194140.19517-1-guro@fb.com
[guro@fb.com: fix indirectly reclaimable memory accounting]
Link: http://lkml.kernel.org/r/20180313125701.7955-1-guro@fb.com
Link: http://lkml.kernel.org/r/20180305133743.12746-5-guro@fb.com
Signed-off-by: Roman Gushchin <guro@fb.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.