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Message-ID: <6e3df002-fd04-4acf-a670-d36d5478921a@lucifer.local>
Date: Fri, 27 Jun 2025 17:28:46 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.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>,
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 1/4] mm: convert FPB_IGNORE_* into FPB_HONOR_*
On Fri, Jun 27, 2025 at 01:55:07PM +0200, David Hildenbrand wrote:
> Honoring these PTE bits is the exception, so let's invert the meaning.
>
> With this change, most callers don't have to pass any flags.
>
> No functional change intended.
>
> Signed-off-by: David Hildenbrand <david@...hat.com>
This is a nice change, it removes a lot of code I really didn't enjoy
looking at for introducing these flags all over the place.
But a nit on the naming below, I'm not a fan of 'honor' here :)
> ---
> mm/internal.h | 16 ++++++++--------
> mm/madvise.c | 3 +--
> mm/memory.c | 11 +++++------
> mm/mempolicy.c | 4 +---
> mm/mlock.c | 3 +--
> mm/mremap.c | 3 +--
> mm/rmap.c | 3 +--
> 7 files changed, 18 insertions(+), 25 deletions(-)
>
> diff --git a/mm/internal.h b/mm/internal.h
> index e84217e27778d..9690c75063881 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -202,17 +202,17 @@ static inline void vma_close(struct vm_area_struct *vma)
> /* Flags for folio_pte_batch(). */
> typedef int __bitwise fpb_t;
>
> -/* Compare PTEs after pte_mkclean(), ignoring the dirty bit. */
> -#define FPB_IGNORE_DIRTY ((__force fpb_t)BIT(0))
> +/* Compare PTEs honoring the dirty bit. */
> +#define FPB_HONOR_DIRTY ((__force fpb_t)BIT(0))
Hm not to be petty but... :)
I'm not sure I find 'honor' very clear here. Ignore is very clear, 'honor' (God
the British English in me wants to say honour here but stipp :P) doesn't
necessarily tell you what is going to happen.
Perhaps PROPAGATE? or OBEY?
>
> -/* Compare PTEs after pte_clear_soft_dirty(), ignoring the soft-dirty bit. */
> -#define FPB_IGNORE_SOFT_DIRTY ((__force fpb_t)BIT(1))
> +/* Compare PTEs honoring the soft-dirty bit. */
> +#define FPB_HONOR_SOFT_DIRTY ((__force fpb_t)BIT(1))
>
> static inline pte_t __pte_batch_clear_ignored(pte_t pte, fpb_t flags)
> {
> - if (flags & FPB_IGNORE_DIRTY)
> + if (!(flags & FPB_HONOR_DIRTY))
> pte = pte_mkclean(pte);
> - if (likely(flags & FPB_IGNORE_SOFT_DIRTY))
> + if (likely(!(flags & FPB_HONOR_SOFT_DIRTY)))
> pte = pte_clear_soft_dirty(pte);
> return pte_wrprotect(pte_mkold(pte));
> }
> @@ -236,8 +236,8 @@ static inline pte_t __pte_batch_clear_ignored(pte_t pte, fpb_t flags)
> * pages of the same large folio.
> *
> * All PTEs inside a PTE batch have the same PTE bits set, excluding the PFN,
> - * the accessed bit, writable bit, dirty bit (with FPB_IGNORE_DIRTY) and
> - * soft-dirty bit (with FPB_IGNORE_SOFT_DIRTY).
> + * 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.
> diff --git a/mm/madvise.c b/mm/madvise.c
> index e61e32b2cd91f..661bb743d2216 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -347,10 +347,9 @@ static inline int madvise_folio_pte_batch(unsigned long addr, unsigned long end,
> pte_t pte, bool *any_young,
> bool *any_dirty)
> {
> - const fpb_t fpb_flags = FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY;
> int max_nr = (end - addr) / PAGE_SIZE;
>
> - return folio_pte_batch(folio, addr, ptep, pte, max_nr, fpb_flags, NULL,
> + return folio_pte_batch(folio, addr, ptep, pte, max_nr, 0, NULL,
> any_young, any_dirty);
> }
>
> diff --git a/mm/memory.c b/mm/memory.c
> index 0f9b32a20e5b7..ab2d6c1425691 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -990,10 +990,10 @@ copy_present_ptes(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma
> * by keeping the batching logic separate.
> */
> if (unlikely(!*prealloc && folio_test_large(folio) && max_nr != 1)) {
> - if (src_vma->vm_flags & VM_SHARED)
> - flags |= FPB_IGNORE_DIRTY;
> - if (!vma_soft_dirty_enabled(src_vma))
> - flags |= FPB_IGNORE_SOFT_DIRTY;
> + if (!(src_vma->vm_flags & VM_SHARED))
> + flags |= FPB_HONOR_DIRTY;
> + if (vma_soft_dirty_enabled(src_vma))
> + flags |= FPB_HONOR_SOFT_DIRTY;
>
> nr = folio_pte_batch(folio, addr, src_pte, pte, max_nr, flags,
> &any_writable, NULL, NULL);
> @@ -1535,7 +1535,6 @@ static inline int zap_present_ptes(struct mmu_gather *tlb,
> struct zap_details *details, int *rss, bool *force_flush,
> bool *force_break, bool *any_skipped)
> {
> - const fpb_t fpb_flags = FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY;
> struct mm_struct *mm = tlb->mm;
> struct folio *folio;
> struct page *page;
> @@ -1565,7 +1564,7 @@ static inline int zap_present_ptes(struct mmu_gather *tlb,
> * by keeping the batching logic separate.
> */
> if (unlikely(folio_test_large(folio) && max_nr != 1)) {
> - nr = folio_pte_batch(folio, addr, pte, ptent, max_nr, fpb_flags,
> + nr = folio_pte_batch(folio, addr, pte, ptent, max_nr, 0,
> NULL, NULL, NULL);
>
> zap_present_folio_ptes(tlb, vma, folio, page, pte, ptent, nr,
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 1ff7b2174eb77..2a25eedc3b1c0 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -675,7 +675,6 @@ static void queue_folios_pmd(pmd_t *pmd, struct mm_walk *walk)
> static int queue_folios_pte_range(pmd_t *pmd, unsigned long addr,
> unsigned long end, struct mm_walk *walk)
> {
> - const fpb_t fpb_flags = FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY;
> struct vm_area_struct *vma = walk->vma;
> struct folio *folio;
> struct queue_pages *qp = walk->private;
> @@ -713,8 +712,7 @@ static int queue_folios_pte_range(pmd_t *pmd, unsigned long addr,
> continue;
> if (folio_test_large(folio) && max_nr != 1)
> nr = folio_pte_batch(folio, addr, pte, ptent,
> - max_nr, fpb_flags,
> - NULL, NULL, NULL);
> + max_nr, 0, NULL, NULL, NULL);
> /*
> * vm_normal_folio() filters out zero pages, but there might
> * still be reserved folios to skip, perhaps in a VDSO.
> diff --git a/mm/mlock.c b/mm/mlock.c
> index 3cb72b579ffd3..2238cdc5eb1c1 100644
> --- a/mm/mlock.c
> +++ b/mm/mlock.c
> @@ -307,14 +307,13 @@ void munlock_folio(struct folio *folio)
> static inline unsigned int folio_mlock_step(struct folio *folio,
> pte_t *pte, unsigned long addr, unsigned long end)
> {
> - const fpb_t fpb_flags = FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY;
> unsigned int count = (end - addr) >> PAGE_SHIFT;
> pte_t ptent = ptep_get(pte);
>
> if (!folio_test_large(folio))
> return 1;
>
> - return folio_pte_batch(folio, addr, pte, ptent, count, fpb_flags, NULL,
> + return folio_pte_batch(folio, addr, pte, ptent, count, 0, NULL,
> NULL, NULL);
> }
>
> diff --git a/mm/mremap.c b/mm/mremap.c
> index 36585041c760d..d4d3ffc931502 100644
> --- a/mm/mremap.c
> +++ b/mm/mremap.c
> @@ -173,7 +173,6 @@ static pte_t move_soft_dirty_pte(pte_t pte)
> static int mremap_folio_pte_batch(struct vm_area_struct *vma, unsigned long addr,
> pte_t *ptep, pte_t pte, int max_nr)
> {
> - const fpb_t flags = FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY;
> struct folio *folio;
>
> if (max_nr == 1)
> @@ -183,7 +182,7 @@ static int mremap_folio_pte_batch(struct vm_area_struct *vma, unsigned long addr
> if (!folio || !folio_test_large(folio))
> return 1;
>
> - return folio_pte_batch(folio, addr, ptep, pte, max_nr, flags, NULL,
> + return folio_pte_batch(folio, addr, ptep, pte, max_nr, 0, NULL,
> NULL, NULL);
> }
>
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 3b74bb19c11dd..a29d7d29c7283 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1849,7 +1849,6 @@ void folio_remove_rmap_pud(struct folio *folio, struct page *page,
> static inline bool can_batch_unmap_folio_ptes(unsigned long addr,
> struct folio *folio, pte_t *ptep)
> {
> - const fpb_t fpb_flags = FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY;
> int max_nr = folio_nr_pages(folio);
> pte_t pte = ptep_get(ptep);
>
> @@ -1860,7 +1859,7 @@ static inline bool can_batch_unmap_folio_ptes(unsigned long addr,
> if (pte_pfn(pte) != folio_pfn(folio))
> return false;
>
> - return folio_pte_batch(folio, addr, ptep, pte, max_nr, fpb_flags, NULL,
> + return folio_pte_batch(folio, addr, ptep, pte, max_nr, 0, NULL,
> NULL, NULL) == max_nr;
I hope a later patch gets rid of this NULL, NULL, NULL... :)
> }
>
> --
> 2.49.0
>
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