diff options
| author | Michal Hocko <mhocko@suse.com> | 2017-07-10 15:49:38 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2017-07-10 16:32:32 -0700 |
| commit | d09b6468824d9e41dc30708475f954e455cf7146 (patch) | |
| tree | 39dcafb5160c681e432749b8dd858bd8559e3982 /Documentation/sysctl | |
| parent | e3d3910a57ab9c70cddb2522ae711ff9bff89e7c (diff) | |
mm: document highmem_is_dirtyable sysctl
It seems that there are still people using 32b kernels which a lot of
memory and the IO tend to suck a lot for them by default. Mostly
because writers are throttled too when the lowmem is used. We have
highmem_is_dirtyable to work around that issue but it seems we never
bothered to document it. Let's do it now, finally.
Link: http://lkml.kernel.org/r/20170626093200.18958-1-mhocko@kernel.org
Signed-off-by: Michal Hocko <mhocko@suse.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Alkis Georgopoulos <alkisg@gmail.com>
Cc: Mel Gorman <mgorman@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation/sysctl')
| -rw-r--r-- | Documentation/sysctl/vm.txt | 20 |
1 files changed, 20 insertions, 0 deletions
diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt index b4ad97f10b8e..48244c42ff52 100644 --- a/Documentation/sysctl/vm.txt +++ b/Documentation/sysctl/vm.txt @@ -240,6 +240,26 @@ fragmentation index is <= extfrag_threshold. The default value is 500. ============================================================== +highmem_is_dirtyable + +Available only for systems with CONFIG_HIGHMEM enabled (32b systems). + +This parameter controls whether the high memory is considered for dirty +writers throttling. This is not the case by default which means that +only the amount of memory directly visible/usable by the kernel can +be dirtied. As a result, on systems with a large amount of memory and +lowmem basically depleted writers might be throttled too early and +streaming writes can get very slow. + +Changing the value to non zero would allow more memory to be dirtied +and thus allow writers to write more data which can be flushed to the +storage more effectively. Note this also comes with a risk of pre-mature +OOM killer because some writers (e.g. direct block device writes) can +only use the low memory and they can fill it up with dirty data without +any throttling. + +============================================================== + hugepages_treat_as_movable This parameter controls whether we can allocate hugepages from ZONE_MOVABLE |