linux-kernel - Re: [PATCHv2 3/5] mm/rmap: mlock large folios in try_to_unmap

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Message-ID: <pdorb325r7fatuclbaw4zriieve4tphlrox6w36fo4mlmzgcx7@kdsf4pwqs2wy>
Date: Mon, 22 Sep 2025 10:51:35 +0100
From: Kiryl Shutsemau <kirill@...temov.name>
To: Shakeel Butt <shakeel.butt@...ux.dev>
Cc: Andrew Morton <akpm@...ux-foundation.org>, 
	David Hildenbrand <david@...hat.com>, Hugh Dickins <hughd@...gle.com>, 
	Matthew Wilcox <willy@...radead.org>, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, 
	"Liam R. Howlett" <Liam.Howlett@...cle.com>, Vlastimil Babka <vbabka@...e.cz>, 
	Mike Rapoport <rppt@...nel.org>, Suren Baghdasaryan <surenb@...gle.com>, 
	Michal Hocko <mhocko@...e.com>, Rik van Riel <riel@...riel.com>, 
	Harry Yoo <harry.yoo@...cle.com>, Johannes Weiner <hannes@...xchg.org>, 
	Baolin Wang <baolin.wang@...ux.alibaba.com>, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2 3/5] mm/rmap: mlock large folios in try_to_unmap_one()

On Fri, Sep 19, 2025 at 02:27:40PM -0700, Shakeel Butt wrote:
> On Fri, Sep 19, 2025 at 01:40:34PM +0100, Kiryl Shutsemau wrote:
> > From: Kiryl Shutsemau <kas@...nel.org>
> > 
> > Currently, try_to_unmap_once() only tries to mlock small folios.
> > 
> > Use logic similar to folio_referenced_one() to mlock large folios:
> > only do this for fully mapped folios and under page table lock that
> > protects all page table entries.
> > 
> > Signed-off-by: Kiryl Shutsemau <kas@...nel.org>
> > ---
> >  mm/rmap.c | 23 ++++++++++++++++++++---
> >  1 file changed, 20 insertions(+), 3 deletions(-)
> > 
> > diff --git a/mm/rmap.c b/mm/rmap.c
> > index 3d0235f332de..482e6504fa88 100644
> > --- a/mm/rmap.c
> > +++ b/mm/rmap.c
> > @@ -1870,6 +1870,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
> >  	unsigned long nr_pages = 1, end_addr;
> >  	unsigned long pfn;
> >  	unsigned long hsz = 0;
> > +	int ptes = 0;
> >  
> >  	/*
> >  	 * When racing against e.g. zap_pte_range() on another cpu,
> > @@ -1910,10 +1911,26 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
> >  		 */
> >  		if (!(flags & TTU_IGNORE_MLOCK) &&
> >  		    (vma->vm_flags & VM_LOCKED)) {
> > +			ptes++;
> > +			ret = false;
> > +
> > +			/* Only mlock fully mapped pages */
> > +			if (pvmw.pte && ptes != pvmw.nr_pages)
> > +				continue;
> > +
> > +			/*
> > +			 * All PTEs must be protected by page table lock in
> > +			 * order to mlock the page.
> > +			 *
> > +			 * If page table boundary has been cross, current ptl
> > +			 * only protect part of ptes.
> > +			 */
> > +			if (pvmw.flags & PVMW_PGTABLE_CROSSSED)
> > +				goto walk_done;
> 
> Should it be goto walk_abort?

I already have to set ret to false above to make it work for partially
mapped large folios. So walk_done is enough here.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov