Commit 1f3ac4c5 authored by David Hildenbrand's avatar David Hildenbrand Committed by Andrew Morton
Browse files

mm/damon: handle device-exclusive entries correctly in damon_folio_mkold_one() 

Ever since commit b756a3b5 ("mm: device exclusive memory access") we
can return with a device-exclusive entry from page_vma_mapped_walk().

damon_folio_mkold_one() is not prepared for that and calls
damon_ptep_mkold() with PFN swap PTEs.  Teach damon_ptep_mkold() to deal
with these PFN swap PTEs.  Note that device-private entries are so far not
applicable on that path, as damon_get_folio() filters out non-lru folios.

Should we just skip PFN swap PTEs completely?  Possible, but it seems
straight forward to just handle it correctly.

Note that we could currently only run into this case with device-exclusive
entries on THPs.  We still adjust the mapcount on conversion to
device-exclusive; this makes the rmap walk abort early for small folios,
because we'll always have !folio_mapped() with a single device-exclusive
entry.  We'll adjust the mapcount logic once all page_vma_mapped_walk()
users can properly handle device-exclusive entries.

Link: https://lkml.kernel.org/r/20250210193801.781278-16-david@redhat.com


Signed-off-by: default avatarDavid Hildenbrand <david@redhat.com>
Reviewed-by: default avatarSeongJae Park <sj@kernel.org>
Tested-by: default avatarAlistair Popple <apopple@nvidia.com>
Cc: Alex Shi <alexs@kernel.org>
Cc: Danilo Krummrich <dakr@kernel.org>
Cc: Dave Airlie <airlied@gmail.com>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Karol Herbst <kherbst@redhat.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Lyude <lyude@redhat.com>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Simona Vetter <simona.vetter@ffwll.ch>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Yanteng Si <si.yanteng@linux.dev>
Cc: Barry Song <v-songbaohua@oppo.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 39628c39

mm/damon/ops-common.c

+21 −2
Original line number Diff line number Diff line
@@ -9,6 +9,8 @@ 
#include <linux/page_idle.h>

#include <linux/pagemap.h>

#include <linux/rmap.h>

#include <linux/swap.h>

#include <linux/swapops.h>



#include "ops-common.h"
@@ -39,12 +41,29 @@ struct folio *damon_get_folio(unsigned long pfn) 


void damon_ptep_mkold(pte_t *pte, struct vm_area_struct *vma, unsigned long addr)

{

	struct folio *folio = damon_get_folio(pte_pfn(ptep_get(pte)));

	pte_t pteval = ptep_get(pte);

	struct folio *folio;

	bool young = false;

	unsigned long pfn;



	if (likely(pte_present(pteval)))

		pfn = pte_pfn(pteval);

	else

		pfn = swp_offset_pfn(pte_to_swp_entry(pteval));



	folio = damon_get_folio(pfn);

	if (!folio)

		return;



	if (ptep_clear_young_notify(vma, addr, pte))

	/*

	 * PFN swap PTEs, such as device-exclusive ones, that actually map pages

	 * are "old" from a CPU perspective. The MMU notifier takes care of any

	 * device aspects.

	 */

	if (likely(pte_present(pteval)))

		young |= ptep_test_and_clear_young(vma, addr, pte);

	young |= mmu_notifier_clear_young(vma->vm_mm, addr, addr + PAGE_SIZE);

	if (young)

		folio_set_young(folio);



	folio_set_idle(folio);