Re: [PATCH] mm/damon: skip folios already on the migration target node

[SJ Park <sj@kernel.org>]

One more trivial nit.  Let's use 'mm/damon/{p,v}addr:' as the subject prefix.

On Wed, 28 Oct 2026 18:01:43 -0700 SJ Park <sj@kernel.org> wrote:

> On Thu, 29 Oct 2026 00:05:46 +1100 Aveline Noir <jm5905938@gmail.com> wrote:
> 
> > While measuring DAMOS migration overhead, I found that the target_nid
> > path isolates folios already on the target node, then puts them back on
> > the LRU without migrating them.
> > 
> > Skip them before isolation in vaddr and paddr, as the vaddr explicit
> > destinations path already does.
> 
> Nice catch!
> 
> > 
> > Signed-off-by: Aveline Noir <jm5905938@gmail.com>
> 
> Other than below trivial nit,
> 
> Reviewed-by: SJ Park <sj@kernel.org>
> 
> > 
> > ---
> > DAMON KUnit and selftests all passed. In a synthetic same-node fvaddr
> > test on a two-node x86-64 KVM guest (8 interleaved runs per kernel),
> > guest-kernel cycles fell by about 29%
> > with 4 KiB regions and 90% with 16 MiB regions. Median kdamond CPU
> > time fell by about 76% with 16 MiB regions, with no clear change
> > with 4 KiB regions.
> 
> Thank you for sharing the test result.  We don't want to add too much test
> results in the commit message.  But the performance part above is informative
> and concise, so I think it deserves to be in the commit message.
> 
> > ---
> >  mm/damon/paddr.c |  2 ++
> >  mm/damon/vaddr.c | 22 ++++++++++++----------
> >  2 files changed, 14 insertions(+), 10 deletions(-)
> [...]
> > @@ -858,8 +860,8 @@ static int damos_va_migrate_pmd_entry(pmd_t *pmd, unsigned long addr,
> >  			goto huge_out;
> >  		if (damos_va_filter_out(s, folio, walk->vma, addr, NULL, pmd))
> >  			goto huge_out;
> > -		damos_va_migrate_dests_add(folio, walk->vma, addr, dests,
> > -				migration_lists);
> > +		damos_va_migrate_dests_add(folio, walk->vma, addr, s,
> > +					   migration_lists);
> 
> Let's not align parameters on parentheses but just give two tabs indentation.
> 
> >  huge_out:
> >  		spin_unlock(ptl);
> >  		return 0;
> > @@ -883,8 +885,8 @@ static int damos_va_migrate_pmd_entry(pmd_t *pmd, unsigned long addr,
> >  			continue;
> >  		if (damos_va_filter_out(s, folio, walk->vma, addr, pte, NULL))
> >  			continue;
> > -		damos_va_migrate_dests_add(folio, walk->vma, addr, dests,
> > -				migration_lists);
> > +		damos_va_migrate_dests_add(folio, walk->vma, addr, s,
> > +					   migration_lists);
> 
> Ditto.
> 
> Assuming you accept my humble suggestions above, I applied  this patch to
> damon/next [1] tree, together with my above suggestions.  I will repost it for
> mm.git inclusion within a week.  So, no action from your side is needed for
> now.  Let me know if you think changes to the plan or discussions are needed.

I also added the suggested subject prefix in damon/next tree.  Please feel free
to let me know if you have an opinion.

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


Thanks,
SJ

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