On Tue, Jan 28, 2025 at 5:50 PM Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx> wrote:
>
> Commit b7c0ccdfbafd ("mm: zswap: support large folios in zswap_store()")
> mistakenly skipped charging any zswapped pages when a single call to
> zswap_store_page() failed, even if some pages in the folio are
> successfully stored in zswap.
>
> Making things worse, these not-charged pages are uncharged in
> zswap_entry_free(), making zswap charging inconsistent.
>
> This inconsistency triggers two warnings when following these steps:
> # On a machine with 64GiB of RAM and 36GiB of zswap
> $ stress-ng --bigheap 2 # wait until the OOM-killer kills stress-ng
> $ sudo reboot
>
> Two warnings are:
> in mm/memcontrol.c:163, function obj_cgroup_release():
> WARN_ON_ONCE(nr_bytes & (PAGE_SIZE - 1));
>
> in mm/page_counter.c:60, function page_counter_cancel():
> if (WARN_ONCE(new < 0, "page_counter underflow: %ld nr_pages=%lu\n",
> new, nr_pages))
>
> Charge zswapped pages even if some pages of the folio are not zswapped.
> After resolving the inconsistency, these warnings disappear.
>
> Fixes: b7c0ccdfbafd ("mm: zswap: support large folios in zswap_store()")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>
> ---
> mm/zswap.c | 12 ++++++------
> 1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/mm/zswap.c b/mm/zswap.c
> index 6504174fbc6a..92752cd05c75 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -1568,20 +1568,20 @@ bool zswap_store(struct folio *folio)
>
> bytes = zswap_store_page(page, objcg, pool);
> if (bytes < 0)
> - goto put_pool;
> + goto charge_zswap;
> compressed_bytes += bytes;
> }
>
> - if (objcg) {
> - obj_cgroup_charge_zswap(objcg, compressed_bytes);
> - count_objcg_events(objcg, ZSWPOUT, nr_pages);
> - }
> -
> atomic_long_add(nr_pages, &zswap_stored_pages);
> count_vm_events(ZSWPOUT, nr_pages);
Wait, it also does not account for these events/counters.
Will send v2. Sorry for the noise.
If I missed anything else, please let me know.
> ret = true;
>
> +charge_zswap:
> + if (objcg) {
> + obj_cgroup_charge_zswap(objcg, compressed_bytes);
> + count_objcg_events(objcg, ZSWPOUT, nr_pages);
> + }
> put_pool:
> zswap_pool_put(pool);
> put_objcg:
> --
> 2.47.1
>
