Commit c843966c authored by Johannes Weiner's avatar Johannes Weiner Committed by Linus Torvalds
Browse files

mm: allow swappiness that prefers reclaiming anon over the file workingset 



With the advent of fast random IO devices (SSDs, PMEM) and in-memory swap
devices such as zswap, it's possible for swap to be much faster than
filesystems, and for swapping to be preferable over thrashing filesystem
caches.

Allow setting swappiness - which defines the rough relative IO cost of
cache misses between page cache and swap-backed pages - to reflect such
situations by making the swap-preferred range configurable.

Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@surriel.com>
Link: http://lkml.kernel.org/r/20200520232525.798933-4-hannes@cmpxchg.org


Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 497a6c1b

Documentation/admin-guide/sysctl/vm.rst

+18 −5
Original line number Diff line number Diff line
@@ -831,14 +831,27 @@ tooling to work, you can do:: 
swappiness

==========



This control is used to define how aggressive the kernel will swap

memory pages.  Higher values will increase aggressiveness, lower values

decrease the amount of swap.  A value of 0 instructs the kernel not to

initiate swap until the amount of free and file-backed pages is less

than the high water mark in a zone.

This control is used to define the rough relative IO cost of swapping

and filesystem paging, as a value between 0 and 200. At 100, the VM

assumes equal IO cost and will thus apply memory pressure to the page

cache and swap-backed pages equally; lower values signify more

expensive swap IO, higher values indicates cheaper.



Keep in mind that filesystem IO patterns under memory pressure tend to

be more efficient than swap's random IO. An optimal value will require

experimentation and will also be workload-dependent.



The default value is 60.



For in-memory swap, like zram or zswap, as well as hybrid setups that

have swap on faster devices than the filesystem, values beyond 100 can

be considered. For example, if the random IO against the swap device

is on average 2x faster than IO from the filesystem, swappiness should

be 133 (x + 2x = 200, 2x = 133.33).



At 0, the kernel will not initiate swap until the amount of free and

file-backed pages is less than the high watermark in a zone.





unprivileged_userfaultfd

========================

kernel/sysctl.c

+2 −1
Original line number Diff line number Diff line
@@ -131,6 +131,7 @@ static unsigned long zero_ul; 
static unsigned long one_ul = 1;

static unsigned long long_max = LONG_MAX;

static int one_hundred = 100;

static int two_hundred = 200;

static int one_thousand = 1000;

#ifdef CONFIG_PRINTK

static int ten_thousand = 10000;
@@ -1391,7 +1392,7 @@ static struct ctl_table vm_table[] = { 
		.mode		= 0644,

		.proc_handler	= proc_dointvec_minmax,

		.extra1		= SYSCTL_ZERO,

		.extra2		= &one_hundred,

		.extra2		= &two_hundred,

	},

#ifdef CONFIG_HUGETLB_PAGE

	{

mm/vmscan.c

+1 −1
Original line number Diff line number Diff line
@@ -161,7 +161,7 @@ struct scan_control { 
#endif



/*

 * From 0 .. 100.  Higher means more swappy.

 * From 0 .. 200.  Higher means more swappy.

 */

int vm_swappiness = 60;

/*

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