| From: Nhat Pham <nphamcs@gmail.com> |
| Subject: zswap: memcontrol: implement zswap writeback disabling (fix) |
| Date: Wed, 20 Dec 2023 16:57:25 -0800 |
| |
| Add a caveat about recurring zswap store failures leading to reclaim |
| inefficiency. |
| |
| Link: https://lkml.kernel.org/r/20231221005725.3446672-1-nphamcs@gmail.com |
| Signed-off-by: Nhat Pham <nphamcs@gmail.com> |
| Suggested-by: Yosry Ahmed <yosryahmed@google.com> |
| Acked-by: Chris Li <chrisl@kernel.org> |
| Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
| --- |
| |
| Documentation/admin-guide/cgroup-v2.rst | 5 ++++- |
| Documentation/admin-guide/mm/zswap.rst | 4 ++++ |
| 2 files changed, 8 insertions(+), 1 deletion(-) |
| |
| --- a/Documentation/admin-guide/cgroup-v2.rst~zswap-memcontrol-implement-zswap-writeback-disabling-fix |
| +++ a/Documentation/admin-guide/cgroup-v2.rst |
| @@ -1686,7 +1686,10 @@ PAGE_SIZE multiple when read back. |
| |
| 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 failure. |
| + 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. |
| --- a/Documentation/admin-guide/mm/zswap.rst~zswap-memcontrol-implement-zswap-writeback-disabling-fix |
| +++ a/Documentation/admin-guide/mm/zswap.rst |
| @@ -159,6 +159,10 @@ zswap itself) on a cgroup-basis as follo |
| |
| echo 0 > /sys/fs/cgroup/<cgroup-name>/memory.zswap.writeback |
| |
| +Note that if the 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). |
| + |
| When there is a sizable amount of cold memory residing in the zswap pool, it |
| can be advantageous to proactively write these cold pages to swap and reclaim |
| the memory for other use cases. By default, the zswap shrinker is disabled. |
| _ |
