| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <51675d77-9453-43cc-bfda-f21a2edfeace@nvidia.com>
Date: Tue, 25 Nov 2025 09:14:21 +1100
From: Balbir Singh <balbirs@...dia.com>
To: Zi Yan <ziy@...dia.com>, David Hildenbrand <david@...nel.org>,
Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Baolin Wang <baolin.wang@...ux.alibaba.com>,
"Liam R. Howlett" <Liam.Howlett@...cle.com>, Nico Pache <npache@...hat.com>,
Ryan Roberts <ryan.roberts@....com>, Dev Jain <dev.jain@....com>,
Barry Song <baohua@...nel.org>, Lance Yang <lance.yang@...ux.dev>,
Miaohe Lin <linmiaohe@...wei.com>, Naoya Horiguchi
<nao.horiguchi@...il.com>, Wei Yang <richard.weiyang@...il.com>,
linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/4] mm/huge_memory: replace can_split_folio() with
direct refcount calculation
On 11/22/25 13:55, Zi Yan wrote:
> can_split_folio() is just a refcount comparison, making sure only the
> split caller holds an extra pin. Open code it with
> folio_expected_ref_count() != folio_ref_count() - 1. For the extra_pins
> used by folio_ref_freeze(), add folio_cache_references() to calculate it.
>
> Suggested-by: David Hildenbrand (Red Hat) <david@...nel.org>
> Signed-off-by: Zi Yan <ziy@...dia.com>
> ---
> include/linux/huge_mm.h | 1 -
> mm/huge_memory.c | 43 ++++++++++++++++-------------------------
> mm/vmscan.c | 3 ++-
> 3 files changed, 19 insertions(+), 28 deletions(-)
>
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index 97686fb46e30..1ecaeccf39c9 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -369,7 +369,6 @@ enum split_type {
> SPLIT_TYPE_NON_UNIFORM,
> };
>
> -bool can_split_folio(struct folio *folio, int caller_pins, int *pextra_pins);
> int __split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
> unsigned int new_order);
> int folio_split_unmapped(struct folio *folio, unsigned int new_order);
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index c1f1055165dd..6c821c1c0ac3 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -3455,23 +3455,6 @@ static void lru_add_split_folio(struct folio *folio, struct folio *new_folio,
> }
> }
>
> -/* Racy check whether the huge page can be split */
> -bool can_split_folio(struct folio *folio, int caller_pins, int *pextra_pins)
> -{
> - int extra_pins;
> -
> - /* Additional pins from page cache */
> - if (folio_test_anon(folio))
> - extra_pins = folio_test_swapcache(folio) ?
> - folio_nr_pages(folio) : 0;
> - else
> - extra_pins = folio_nr_pages(folio);
> - if (pextra_pins)
> - *pextra_pins = extra_pins;
> - return folio_mapcount(folio) == folio_ref_count(folio) - extra_pins -
> - caller_pins;
> -}
> -
> static bool page_range_has_hwpoisoned(struct page *page, long nr_pages)
> {
> for (; nr_pages; page++, nr_pages--)
> @@ -3776,17 +3759,26 @@ int folio_check_splittable(struct folio *folio, unsigned int new_order,
> return 0;
> }
>
> +/* Number of folio references from the pagecache or the swapcache. */
> +static unsigned int folio_cache_references(const struct folio *folio)
folio_cache_ref_count?
> +{
> + if (folio_test_anon(folio) && !folio_test_swapcache(folio))
> + return 0;
> + return folio_nr_pages(folio);
> +}
> +
Does this belong to include/linux/mm.h with the other helpers?
> static int __folio_freeze_and_split_unmapped(struct folio *folio, unsigned int new_order,
> struct page *split_at, struct xa_state *xas,
> struct address_space *mapping, bool do_lru,
> struct list_head *list, enum split_type split_type,
> - pgoff_t end, int *nr_shmem_dropped, int extra_pins)
> + pgoff_t end, int *nr_shmem_dropped)
> {
> struct folio *end_folio = folio_next(folio);
> struct folio *new_folio, *next;
> int old_order = folio_order(folio);
> int ret = 0;
> struct deferred_split *ds_queue;
> + int extra_pins = folio_cache_references(folio);
>
> VM_WARN_ON_ONCE(!mapping && end);
> /* Prevent deferred_split_scan() touching ->_refcount */
> @@ -3956,7 +3948,7 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
> struct folio *new_folio, *next;
> int nr_shmem_dropped = 0;
> int remap_flags = 0;
> - int extra_pins, ret;
> + int ret;
> pgoff_t end = 0;
>
> VM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio);
> @@ -4036,7 +4028,7 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
> * Racy check if we can split the page, before unmap_folio() will
> * split PMDs
> */
> - if (!can_split_folio(folio, 1, &extra_pins)) {
> + if (folio_expected_ref_count(folio) != folio_ref_count(folio) - 1) {
> ret = -EAGAIN;
> goto out_unlock;
> }
> @@ -4059,8 +4051,7 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
> }
>
> ret = __folio_freeze_and_split_unmapped(folio, new_order, split_at, &xas, mapping,
> - true, list, split_type, end, &nr_shmem_dropped,
> - extra_pins);
> + true, list, split_type, end, &nr_shmem_dropped);
> fail:
> if (mapping)
> xas_unlock(&xas);
> @@ -4134,20 +4125,20 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
> */
> int folio_split_unmapped(struct folio *folio, unsigned int new_order)
> {
> - int extra_pins, ret = 0;
> + int ret = 0;
>
> VM_WARN_ON_ONCE_FOLIO(folio_mapped(folio), folio);
> VM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio);
> VM_WARN_ON_ONCE_FOLIO(!folio_test_large(folio), folio);
> VM_WARN_ON_ONCE_FOLIO(!folio_test_anon(folio), folio);
>
> - if (!can_split_folio(folio, 1, &extra_pins))
> + if (folio_expected_ref_count(folio) != folio_ref_count(folio) - 1)
> return -EAGAIN;
>
> local_irq_disable();
> ret = __folio_freeze_and_split_unmapped(folio, new_order, &folio->page, NULL,
> NULL, false, NULL, SPLIT_TYPE_UNIFORM,
> - 0, NULL, extra_pins);
> + 0, NULL);
> local_irq_enable();
> return ret;
> }
> @@ -4640,7 +4631,7 @@ static int split_huge_pages_pid(int pid, unsigned long vaddr_start,
> * can be split or not. So skip the check here.
> */
> if (!folio_test_private(folio) &&
> - !can_split_folio(folio, 0, NULL))
> + folio_expected_ref_count(folio) != folio_ref_count(folio))
> goto next;
>
> if (!folio_trylock(folio))
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 92980b072121..3b85652a42b9 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1284,7 +1284,8 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
> goto keep_locked;
> if (folio_test_large(folio)) {
> /* cannot split folio, skip it */
> - if (!can_split_folio(folio, 1, NULL))
> + if (folio_expected_ref_count(folio) !=
> + folio_ref_count(folio) - 1)
> goto activate_locked;
> /*
> * Split partially mapped folios right away.
Otherwise, LGTM
Acked-by: Balbir Singh <balbirs@...dia.com>
Powered by blists - more mailing lists