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Message-ID: <CAGsJ_4z+1n3cu35iyAiXz_W4_XCxW0PoHbo4CVnuJBEgDadQ0w@mail.gmail.com>
Date: Mon, 26 Dec 2022 22:40:49 +1300
From: Barry Song <baohua@...nel.org>
To: Chih-En Lin <shiyn.lin@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Qi Zheng <zhengqi.arch@...edance.com>,
David Hildenbrand <david@...hat.com>,
Matthew Wilcox <willy@...radead.org>,
Christophe Leroy <christophe.leroy@...roup.eu>,
John Hubbard <jhubbard@...dia.com>,
Nadav Amit <namit@...are.com>, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, Steven Rostedt <rostedt@...dmis.org>,
Masami Hiramatsu <mhiramat@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Jiri Olsa <jolsa@...nel.org>,
Namhyung Kim <namhyung@...nel.org>,
Yang Shi <shy828301@...il.com>, Peter Xu <peterx@...hat.com>,
"Zach O'Keefe" <zokeefe@...gle.com>,
"Liam R . Howlett" <Liam.Howlett@...cle.com>,
Alex Sierra <alex.sierra@....com>,
Xianting Tian <xianting.tian@...ux.alibaba.com>,
Colin Cross <ccross@...gle.com>,
Suren Baghdasaryan <surenb@...gle.com>,
Pasha Tatashin <pasha.tatashin@...een.com>,
Suleiman Souhlal <suleiman@...gle.com>,
Brian Geffon <bgeffon@...gle.com>, Yu Zhao <yuzhao@...gle.com>,
Tong Tiangen <tongtiangen@...wei.com>,
Liu Shixin <liushixin2@...wei.com>,
Li kunyu <kunyu@...china.com>,
Anshuman Khandual <anshuman.khandual@....com>,
Vlastimil Babka <vbabka@...e.cz>,
Hugh Dickins <hughd@...gle.com>,
Minchan Kim <minchan@...nel.org>,
Miaohe Lin <linmiaohe@...wei.com>,
Gautam Menghani <gautammenghani201@...il.com>,
Catalin Marinas <catalin.marinas@....com>,
Mark Brown <broonie@...nel.org>, Will Deacon <will@...nel.org>,
"Eric W . Biederman" <ebiederm@...ssion.com>,
Thomas Gleixner <tglx@...utronix.de>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Andy Lutomirski <luto@...nel.org>,
Fenghua Yu <fenghua.yu@...el.com>,
Barret Rhoden <brho@...gle.com>,
Davidlohr Bueso <dave@...olabs.net>,
"Jason A . Donenfeld" <Jason@...c4.com>,
Dinglan Peng <peng301@...due.edu>,
Pedro Fonseca <pfonseca@...due.edu>,
Jim Huang <jserv@...s.ncku.edu.tw>,
Huichun Feng <foxhoundsk.tw@...il.com>
Subject: Re: [PATCH v3 04/14] mm/rmap: Break COW PTE in rmap walking
On Tue, Dec 20, 2022 at 8:25 PM Chih-En Lin <shiyn.lin@...il.com> wrote:
>
> Some of the features (unmap, migrate, device exclusive, mkclean, etc)
> might modify the pte entry via rmap. Add a new page vma mapped walk
> flag, PVMW_BREAK_COW_PTE, to indicate the rmap walking to break COW PTE.
>
> Signed-off-by: Chih-En Lin <shiyn.lin@...il.com>
> ---
> include/linux/rmap.h | 2 ++
> mm/migrate.c | 3 ++-
> mm/page_vma_mapped.c | 2 ++
> mm/rmap.c | 12 +++++++-----
> mm/vmscan.c | 7 ++++++-
> 5 files changed, 19 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/rmap.h b/include/linux/rmap.h
> index bd3504d11b155..d0f07e5519736 100644
> --- a/include/linux/rmap.h
> +++ b/include/linux/rmap.h
> @@ -368,6 +368,8 @@ int make_device_exclusive_range(struct mm_struct *mm, unsigned long start,
> #define PVMW_SYNC (1 << 0)
> /* Look for migration entries rather than present PTEs */
> #define PVMW_MIGRATION (1 << 1)
> +/* Break COW-ed PTE during walking */
> +#define PVMW_BREAK_COW_PTE (1 << 2)
>
> struct page_vma_mapped_walk {
> unsigned long pfn;
> diff --git a/mm/migrate.c b/mm/migrate.c
> index dff333593a8ae..a4be7e04c9b09 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -174,7 +174,8 @@ void putback_movable_pages(struct list_head *l)
> static bool remove_migration_pte(struct folio *folio,
> struct vm_area_struct *vma, unsigned long addr, void *old)
> {
> - DEFINE_FOLIO_VMA_WALK(pvmw, old, vma, addr, PVMW_SYNC | PVMW_MIGRATION);
> + DEFINE_FOLIO_VMA_WALK(pvmw, old, vma, addr,
> + PVMW_SYNC | PVMW_MIGRATION | PVMW_BREAK_COW_PTE);
>
> while (page_vma_mapped_walk(&pvmw)) {
> rmap_t rmap_flags = RMAP_NONE;
> diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
> index 93e13fc17d3cb..5dfc9236dc505 100644
> --- a/mm/page_vma_mapped.c
> +++ b/mm/page_vma_mapped.c
> @@ -251,6 +251,8 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
> step_forward(pvmw, PMD_SIZE);
> continue;
> }
> + if (pvmw->flags & PVMW_BREAK_COW_PTE)
> + break_cow_pte(vma, pvmw->pmd, pvmw->address);
> if (!map_pte(pvmw))
> goto next_pte;
> this_pte:
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 2ec925e5fa6a9..b1b7dcbd498be 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -807,7 +807,8 @@ static bool folio_referenced_one(struct folio *folio,
> struct vm_area_struct *vma, unsigned long address, void *arg)
> {
> struct folio_referenced_arg *pra = arg;
> - DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, 0);
> + /* it will clear the entry, so we should break COW PTE. */
> + DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, PVMW_BREAK_COW_PTE);
what do you mean by breaking cow pte? in memory reclamation case, we are only
checking and clearing page referenced bit in pte, do we really need to
break cow?
> int referenced = 0;
>
> while (page_vma_mapped_walk(&pvmw)) {
> @@ -1012,7 +1013,8 @@ static int page_vma_mkclean_one(struct page_vma_mapped_walk *pvmw)
> static bool page_mkclean_one(struct folio *folio, struct vm_area_struct *vma,
> unsigned long address, void *arg)
> {
> - DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, PVMW_SYNC);
> + DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address,
> + PVMW_SYNC | PVMW_BREAK_COW_PTE);
> int *cleaned = arg;
>
> *cleaned += page_vma_mkclean_one(&pvmw);
> @@ -1471,7 +1473,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
> unsigned long address, void *arg)
> {
> struct mm_struct *mm = vma->vm_mm;
> - DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, 0);
> + DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, PVMW_BREAK_COW_PTE);
> pte_t pteval;
> struct page *subpage;
> bool anon_exclusive, ret = true;
> @@ -1842,7 +1844,7 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
> unsigned long address, void *arg)
> {
> struct mm_struct *mm = vma->vm_mm;
> - DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, 0);
> + DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, PVMW_BREAK_COW_PTE);
> pte_t pteval;
> struct page *subpage;
> bool anon_exclusive, ret = true;
> @@ -2195,7 +2197,7 @@ static bool page_make_device_exclusive_one(struct folio *folio,
> struct vm_area_struct *vma, unsigned long address, void *priv)
> {
> struct mm_struct *mm = vma->vm_mm;
> - DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, 0);
> + DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, PVMW_BREAK_COW_PTE);
> struct make_exclusive_args *args = priv;
> pte_t pteval;
> struct page *subpage;
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 026199c047e0e..980d2056adfd1 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1781,6 +1781,10 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
> }
> }
>
> + /*
> + * Break COW PTE since checking the reference
> + * of folio might modify the PTE.
> + */
> if (!ignore_references)
> references = folio_check_references(folio, sc);
>
> @@ -1864,7 +1868,8 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
>
> /*
> * The folio is mapped into the page tables of one or more
> - * processes. Try to unmap it here.
> + * processes. Try to unmap it here. Also, since it will write
> + * to the page tables, break COW PTE if they are.
> */
> if (folio_mapped(folio)) {
> enum ttu_flags flags = TTU_BATCH_FLUSH;
> --
> 2.37.3
>
Thanks
Barry
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