Re: [PATCH v3] mm/damon/ops-common: putback folios on invalid migrate nid

On Sun, 26 Jul 2026 09:48:15 +0800 [email protected] wrote:

> From: liyouhong <[email protected]>
> 
> damon_pa_migrate() and damos_va_migrate() isolate folios into a local list
> and then call damon_migrate_pages().  When target_nid is invalid (including
> the scheme default NUMA_NO_NODE / -1), damon_migrate_pages() returns early
> without putting the folios back to the LRU.
> 
> Callers then discard the list head while those folios remain isolated with
> an extra reference taken by folio_isolate_lru().  The pages stay off the
> LRU for as long as the mapping exists (anon active+inactive counts drop
> while RSS does not), and the leftover references can pin the pages after
> the mapping is gone.
> 
> Put the folios back on the invalid-nid path so ignored migration requests
> still return them to the LRU.

Looks good to me, thank you for catching and fixing this, liyouhong!

Andrew, I think this deserves the hotfix fast track.  The bug can cause memory
pressure, and can be reliably reproduced by the user.  The user should already
have a sysfs write permission, though.  Let me know if you think differently.

This patch is applied to damon/next [1] tree.  If this patch is not added to
mm.git in short term (~1 week?), I will ask mm.git maintainer (Andrew Morton)
to pick this.  So, no action from your side is needed for now.  If it seems I
also forgot doing that or you cannot wait for my action, please feel free to
directly ask that to Andrew.

[1] https://origin.kernel.org/doc/html/latest/mm/damon/maintainer-profile.html#scm-trees


Thanks,
SJ