Re: [PATCH 1/3] mm/vmscan: fix anon-only reclaim evicting file pages when swappiness=max

Re: [PATCH 1/3] mm/vmscan: fix anon-only reclaim evicting file pages when swappiness=max

[Shakeel Butt]

On Fri, Jul 17, 2026 at 07:32:58PM +0800, Ridong wrote:
> From: Ridong Chen <chenridong@xiaomi.com>
> 
> As Qi mentioned [1], when swappiness=max (SWAPPINESS_ANON_ONLY) is set,
> the reclaim logic is expected to reclaim anonymous pages exclusively.
> However, due to the current ordering of checks in get_scan_count(),
> file pages may still be evicted if can_reclaim_anon_pages() returns
> false, which contradicts the semantics of SWAPPINESS_ANON_ONLY.
> 
> Reproducer in a cgroup holding 64M of file cache, with no swap configured:
> 
>   Before (file cache is wrongly evicted):
>     # cat memory.stat
>     anon 196608
>     file 67178496
>     pgscan_proactive 0
>     # echo "64M swappiness=max" > memory.reclaim
>     # cat memory.stat
>     anon 208896
>     file 4096                 <- page cache evicted
>     pgsteal_proactive 16400
>     pgscan_proactive 16400
> 
>   After (file cache is left intact):
>     # cat memory.stat
>     anon 200704
>     file 67178496
>     pgscan_proactive 0
>     # echo "64M swappiness=max" > memory.reclaim
>     -bash: echo: write error: Resource temporarily unavailable
>     # cat memory.stat
>     anon 208896
>     file 67178496             <- page cache untouched
>     pgsteal_proactive 0
>     pgscan_proactive 0
> 
> Fix this by bailing out early when SWAPPINESS_ANON_ONLY is set and no
> anonymous pages are reclaimable, before falling back to file reclaim.
> 
> [1] https://lore.kernel.org/cgroups/7ddf3eee-5fe2-45f7-8614-c8936a039e04@linux.dev/
> 
> Fixes: 68a1436bde00 ("mm: add swappiness=max arg to memory.reclaim for only anon reclaim")
> Suggested-by: Qi Zheng <qi.zheng@linux.dev>
> Signed-off-by: Ridong Chen <chenridong@xiaomi.com>

Acked-by: Shakeel Butt <shakeel.butt@linux.dev>

Re: [PATCH 2/3] mm: vmscan: propagate real error code from per-node proactive reclaim

[Shakeel Butt]

On Fri, Jul 17, 2026 at 07:32:59PM +0800, Ridong wrote:
> From: Ridong Chen <chenridong@xiaomi.com>
> 
> It has been observed that per-node proactive reclaim always returns
> -EAGAIN when any error occurs. As discussed in the mailing list [1],
> the interface should distinguish between cases where no reclaimable
> memory is left and where another entity is concurrently using the
> same interface. Propagate the real error code, consistent with how
> memcg proactive reclaim handles errors.
> 
> [1] https://lore.kernel.org/all/20250717235604.2atyx2aobwowpge3@offworld/T/#m3514718be82a31b05726a49da9b61fbfc69a589e
> 
> Fixes: b980077899ea ("mm: introduce per-node proactive reclaim interface")
> Signed-off-by: Ridong Chen <chenridong@xiaomi.com>

Acked-by: Shakeel Butt <shakeel.butt@linux.dev>

Re: [PATCH 3/3] mm: vmscan: drop unused gfp_mask parameter from __node_reclaim()

[Shakeel Butt]

On Fri, Jul 17, 2026 at 07:33:00PM +0800, Ridong wrote:
> From: Ridong Chen <chenridong@xiaomi.com>
> 
> Commit 57972c78e678 ("mm/vmscan: make __node_reclaim() more generic")
> moved the scan_control construction out to the callers and passed the
> struct in by pointer.  After that change every use of the gfp mask inside
> __node_reclaim() goes through sc->gfp_mask, leaving the gfp_mask parameter
> unused. Just remove the dead parameter and update the callers accordingly.
> No functional change.
> 
> Signed-off-by: Ridong Chen <chenridong@xiaomi.com>

Acked-by: Shakeel Butt <shakeel.butt@linux.dev>

Re: [PATCH 0/3] mm/vmscan: fix swappiness=max and clean up per-node proactive reclaim

[Andrew Morton]

On Fri, 17 Jul 2026 19:32:57 +0800 Ridong <ridong.chen@linux.dev> wrote:

> From: Ridong Chen <chenridong@xiaomi.com>
> 
> Two fixes and one cleanup.
> 
> Patch 1 fixes "swappiness=max": the anon-only test in get_scan_count()
> sat after the "cannot reclaim anon" check, so when no anon was
> reclaimable the request fell back to SCAN_FILE and evicted page cache
> instead.
> 
> Patch 2 fixes reclaim_store() collapsing every error into -EAGAIN, so
> callers can no longer tell an invalid argument from a busy interface;
> propagate the real error code, matching the memcg path.
> 
> Patch 3 drops the now-unused gfp_mask parameter from __node_reclaim().

Thanks.  Sashiko want to know whether MGLRU should also be fixed:
	https://sashiko.dev/#/patchset/20260717113300.214717-1-ridong.chen@linux.dev