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Message-ID: <CABzRoyZKgWm=uQ2FioFyxStH+5z5OenX+BKEbfDQg+1546dsHg@mail.gmail.com>
Date: Fri, 27 Jun 2025 21:58:00 +0800
From: Lance Yang <ioworker0@...il.com>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
Andrew Morton <akpm@...ux-foundation.org>, "Liam R. Howlett" <Liam.Howlett@...cle.com>,
Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Vlastimil Babka <vbabka@...e.cz>,
Jann Horn <jannh@...gle.com>, Mike Rapoport <rppt@...nel.org>,
Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>, Zi Yan <ziy@...dia.com>,
Matthew Brost <matthew.brost@...el.com>, Joshua Hahn <joshua.hahnjy@...il.com>,
Rakie Kim <rakie.kim@...com>, Byungchul Park <byungchul@...com>, Gregory Price <gourry@...rry.net>,
Ying Huang <ying.huang@...ux.alibaba.com>, Alistair Popple <apopple@...dia.com>,
Pedro Falcato <pfalcato@...e.de>, Rik van Riel <riel@...riel.com>, Harry Yoo <harry.yoo@...cle.com>
Subject: Re: [PATCH v1 2/4] mm: smaller folio_pte_batch() improvements
On Fri, Jun 27, 2025 at 7:55 PM David Hildenbrand <david@...hat.com> wrote:
>
> Let's clean up a bit:
>
> (1) No need for start_ptep vs. ptep anymore, we can simply use ptep
>
> (2) Let's switch to "unsigned int" for everything
>
> (3) We can simplify the code by leaving the pte unchanged after the
> pte_same() check.
>
> (4) Clarify that we should never exceed a single VMA; it indicates a
> problem in the caller.
>
> No functional change intended.
Nice cleanup! Simplifying the loop and removing the temporary variables
makes the code much easier to follow.
Also, clarifying the caller's responsibility to stay within a single VMA
and page table is a nice change ;)
Feel free to add:
Reviewed-by: Lance Yang <lance.yang@...ux.dev>
Thanks,
Lance
>
> Signed-off-by: David Hildenbrand <david@...hat.com>
> ---
> mm/internal.h | 37 +++++++++++++++----------------------
> 1 file changed, 15 insertions(+), 22 deletions(-)
>
> diff --git a/mm/internal.h b/mm/internal.h
> index 9690c75063881..ca6590c6d9eab 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -221,7 +221,7 @@ static inline pte_t __pte_batch_clear_ignored(pte_t pte, fpb_t flags)
> * folio_pte_batch - detect a PTE batch for a large folio
> * @folio: The large folio to detect a PTE batch for.
> * @addr: The user virtual address the first page is mapped at.
> - * @start_ptep: Page table pointer for the first entry.
> + * @ptep: Page table pointer for the first entry.
> * @pte: Page table entry for the first page.
> * @max_nr: The maximum number of table entries to consider.
> * @flags: Flags to modify the PTE batch semantics.
> @@ -233,24 +233,24 @@ static inline pte_t __pte_batch_clear_ignored(pte_t pte, fpb_t flags)
> * first one is dirty.
> *
> * Detect a PTE batch: consecutive (present) PTEs that map consecutive
> - * pages of the same large folio.
> + * pages of the same large folio in a single VMA and a single page table.
> *
> * All PTEs inside a PTE batch have the same PTE bits set, excluding the PFN,
> * the accessed bit, writable bit, dirty bit (unless FPB_HONOR_DIRTY is set) and
> * soft-dirty bit (unless FPB_HONOR_SOFT_DIRTY is set).
> *
> - * start_ptep must map any page of the folio. max_nr must be at least one and
> - * must be limited by the caller so scanning cannot exceed a single page table.
> + * @ptep must map any page of the folio. max_nr must be at least one and
> + * must be limited by the caller so scanning cannot exceed a single VMA and
> + * a single page table.
> *
> * Return: the number of table entries in the batch.
> */
> -static inline int folio_pte_batch(struct folio *folio, unsigned long addr,
> - pte_t *start_ptep, pte_t pte, int max_nr, fpb_t flags,
> +static inline unsigned int folio_pte_batch(struct folio *folio, unsigned long addr,
> + pte_t *ptep, pte_t pte, unsigned int max_nr, fpb_t flags,
> bool *any_writable, bool *any_young, bool *any_dirty)
> {
> - pte_t expected_pte, *ptep;
> - bool writable, young, dirty;
> - int nr, cur_nr;
> + unsigned int nr, cur_nr;
> + pte_t expected_pte;
>
> if (any_writable)
> *any_writable = false;
> @@ -267,29 +267,22 @@ static inline int folio_pte_batch(struct folio *folio, unsigned long addr,
> max_nr = min_t(unsigned long, max_nr,
> folio_pfn(folio) + folio_nr_pages(folio) - pte_pfn(pte));
>
> - nr = pte_batch_hint(start_ptep, pte);
> + nr = pte_batch_hint(ptep, pte);
> expected_pte = __pte_batch_clear_ignored(pte_advance_pfn(pte, nr), flags);
> - ptep = start_ptep + nr;
> + ptep = ptep + nr;
>
> while (nr < max_nr) {
> pte = ptep_get(ptep);
> - if (any_writable)
> - writable = !!pte_write(pte);
> - if (any_young)
> - young = !!pte_young(pte);
> - if (any_dirty)
> - dirty = !!pte_dirty(pte);
> - pte = __pte_batch_clear_ignored(pte, flags);
>
> - if (!pte_same(pte, expected_pte))
> + if (!pte_same(__pte_batch_clear_ignored(pte, flags), expected_pte))
> break;
>
> if (any_writable)
> - *any_writable |= writable;
> + *any_writable |= pte_write(pte);
> if (any_young)
> - *any_young |= young;
> + *any_young |= pte_young(pte);
> if (any_dirty)
> - *any_dirty |= dirty;
> + *any_dirty |= pte_dirty(pte);
>
> cur_nr = pte_batch_hint(ptep, pte);
> expected_pte = pte_advance_pfn(expected_pte, cur_nr);
> --
> 2.49.0
>
>
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