Hi Nhat, Acked-by: Chris Li <chrisl@xxxxxxxxxx> I think a follow up step would be having some patches to address it rather than document it that oh yes, we have a problem in that situation. Chris On Wed, Dec 20, 2023 at 4:57 PM Nhat Pham <nphamcs@xxxxxxxxx> wrote: > > Add a caveat about recurring zswap store failures leading to reclaim > inefficiency. > > Suggested-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx> > Signed-off-by: Nhat Pham <nphamcs@xxxxxxxxx> > --- > Documentation/admin-guide/cgroup-v2.rst | 5 ++++- > Documentation/admin-guide/mm/zswap.rst | 4 ++++ > 2 files changed, 8 insertions(+), 1 deletion(-) > > diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst > index 2b4ac43efdc8..5ec7dd753cd1 100644 > --- a/Documentation/admin-guide/cgroup-v2.rst > +++ b/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. > diff --git a/Documentation/admin-guide/mm/zswap.rst b/Documentation/admin-guide/mm/zswap.rst > index cfa653130346..b42132969e31 100644 > --- a/Documentation/admin-guide/mm/zswap.rst > +++ b/Documentation/admin-guide/mm/zswap.rst > @@ -159,6 +159,10 @@ zswap itself) on a cgroup-basis as follows: > > 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. > -- > 2.34.1 >
