summaryrefslogtreecommitdiff
path: root/Documentation/admin-guide/cgroup-v2.rst
diff options
context:
space:
mode:
authorNhat Pham <nphamcs@gmail.com>2023-12-07 22:24:06 +0300
committerAndrew Morton <akpm@linux-foundation.org>2023-12-30 07:22:11 +0300
commit501a06fe8e4c185bbda371b8cedbdf1b23a633d8 (patch)
tree4aefe7c3ca0b38f8f0e99dc11f38c83d7b66cc1b /Documentation/admin-guide/cgroup-v2.rst
parent1ae41dffd48a700f4bf69e5377f4311de7d92b78 (diff)
downloadlinux-501a06fe8e4c185bbda371b8cedbdf1b23a633d8.tar.xz
zswap: memcontrol: implement zswap writeback disabling
During our experiment with zswap, we sometimes observe swap IOs due to occasional zswap store failures and writebacks-to-swap. These swapping IOs prevent many users who cannot tolerate swapping from adopting zswap to save memory and improve performance where possible. This patch adds the option to disable this behavior entirely: do not writeback to backing swapping device when a zswap store attempt fail, and do not write pages in the zswap pool back to the backing swap device (both when the pool is full, and when the new zswap shrinker is called). This new behavior can be opted-in/out on a per-cgroup basis via a new cgroup file. By default, writebacks to swap device is enabled, which is the previous behavior. Initially, writeback is enabled for the root cgroup, and a newly created cgroup will inherit the current setting of its parent. Note that this is subtly different from setting memory.swap.max to 0, as it still allows for pages to be stored in the zswap pool (which itself consumes swap space in its current form). This patch should be applied on top of the zswap shrinker series: https://lore.kernel.org/linux-mm/20231130194023.4102148-1-nphamcs@gmail.com/ as it also disables the zswap shrinker, a major source of zswap writebacks. For the most part, this feature is motivated by internal parties who have already established their opinions regarding swapping - the workloads that are highly sensitive to IO, and especially those who are using servers with really slow disk performance (for instance, massive but slow HDDs). For these folks, it's impossible to convince them to even entertain zswap if swapping also comes as a packaged deal. Writeback disabling is quite a useful feature in these situations - on a mixed workloads deployment, they can disable writeback for the more IO-sensitive workloads, and enable writeback for other background workloads. For instance, on a server with HDD, I allocate memories and populate them with random values (so that zswap store will always fail), and specify memory.high low enough to trigger reclaim. The time it takes to allocate the memories and just read through it a couple of times (doing silly things like computing the values' average etc.): zswap.writeback disabled: real 0m30.537s user 0m23.687s sys 0m6.637s 0 pages swapped in 0 pages swapped out zswap.writeback enabled: real 0m45.061s user 0m24.310s sys 0m8.892s 712686 pages swapped in 461093 pages swapped out (the last two lines are from vmstat -s). [nphamcs@gmail.com: add a comment about recurring zswap store failures leading to reclaim inefficiency] Link: https://lkml.kernel.org/r/20231221005725.3446672-1-nphamcs@gmail.com Link: https://lkml.kernel.org/r/20231207192406.3809579-1-nphamcs@gmail.com Signed-off-by: Nhat Pham <nphamcs@gmail.com> Suggested-by: Johannes Weiner <hannes@cmpxchg.org> Reviewed-by: Yosry Ahmed <yosryahmed@google.com> Acked-by: Chris Li <chrisl@kernel.org> Cc: Dan Streetman <ddstreet@ieee.org> Cc: David Heidelberg <david@ixit.cz> Cc: Domenico Cerasuolo <cerasuolodomenico@gmail.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Cc: Michal Hocko <mhocko@kernel.org> Cc: Mike Rapoport (IBM) <rppt@kernel.org> Cc: Muchun Song <muchun.song@linux.dev> Cc: Roman Gushchin <roman.gushchin@linux.dev> Cc: Sergey Senozhatsky <senozhatsky@chromium.org> Cc: Seth Jennings <sjenning@redhat.com> Cc: Shakeel Butt <shakeelb@google.com> Cc: Tejun Heo <tj@kernel.org> Cc: Vitaly Wool <vitaly.wool@konsulko.com> Cc: Zefan Li <lizefan.x@bytedance.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'Documentation/admin-guide/cgroup-v2.rst')
-rw-r--r--Documentation/admin-guide/cgroup-v2.rst15
1 files changed, 15 insertions, 0 deletions
diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index 3f85254f3cef..5ec7dd753cd1 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -1679,6 +1679,21 @@ PAGE_SIZE multiple when read back.
limit, it will refuse to take any more stores before existing
entries fault back in or are written out to disk.
+ memory.zswap.writeback
+ A read-write single value file. The default value is "1". The
+ initial value of the root cgroup is 1, and when a new cgroup is
+ created, it inherits the current value of its parent.
+
+ When this is set to 0, all swapping attempts to swapping devices
+ are disabled. This included both zswap writebacks, and swapping due
+ to zswap store failures. If the zswap store failures are recurring
+ (for e.g if the pages are incompressible), users can observe
+ reclaim inefficiency after disabling writeback (because the same
+ pages might be rejected again and again).
+
+ Note that this is subtly different from setting memory.swap.max to
+ 0, as it still allows for pages to be written to the zswap pool.
+
memory.pressure
A read-only nested-keyed file.