Re: [PATCH v1 18/36] mm/gup: drop nth_page() usage within folio when recording subpages
From: David Hildenbrand <hidden>
Date: 2025-09-01 11:35:12
Also in:
dri-devel, intel-gfx, io-uring, kvm, linux-arm-kernel, linux-crypto, linux-ide, linux-iommu, linux-kselftest, linux-mips, linux-mm, linux-mmc, linux-riscv, linux-s390, linux-scsi, lkml, virtualization
Subsystem:
memory management, memory management - gup (get user pages), the rest · Maintainers:
Andrew Morton, David Hildenbrand, Linus Torvalds
quoted
The nice thing is that we only record pages in the array if they actually passed our tests.Yeah that's nice actually. This is fine (not the meme :P)
:D
So yes let's do this!
That leaves us with the following on top of this patch: From 4533c6e3590cab0c53e81045624d5949e0ad9015 Mon Sep 17 00:00:00 2001 From: David Hildenbrand <redacted> Date: Fri, 29 Aug 2025 15:41:45 +0200 Subject: [PATCH] mm/gup: remove record_subpages() We can just cleanup the code by calculating the #refs earlier, so we can just inline what remains of record_subpages(). Calculate the number of references/pages ahead of times, and record them only once all our tests passed. Signed-off-by: David Hildenbrand <redacted> --- mm/gup.c | 25 ++++++++----------------- 1 file changed, 8 insertions(+), 17 deletions(-)
diff --git a/mm/gup.c b/mm/gup.c
index 89ca0813791ab..5a72a135ec70b 100644
--- a/mm/gup.c
+++ b/mm/gup.c@@ -484,19 +484,6 @@ static inline void mm_set_has_pinned_flag(struct mm_struct *mm) #ifdef CONFIG_MMU #ifdef CONFIG_HAVE_GUP_FAST -static int record_subpages(struct page *page, unsigned long sz, - unsigned long addr, unsigned long end, - struct page **pages) -{ - int nr; - - page += (addr & (sz - 1)) >> PAGE_SHIFT; - for (nr = 0; addr != end; nr++, addr += PAGE_SIZE) - pages[nr] = page++; - - return nr; -} - /** * try_grab_folio_fast() - Attempt to get or pin a folio in fast path. * @page: pointer to page to be grabbed
@@ -2963,8 +2950,8 @@ static int gup_fast_pmd_leaf(pmd_t orig, pmd_t *pmdp, unsigned long addr, if (pmd_special(orig)) return 0; - page = pmd_page(orig); - refs = record_subpages(page, PMD_SIZE, addr, end, pages + *nr); + refs = (end - addr) >> PAGE_SHIFT; + page = pmd_page(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT); folio = try_grab_folio_fast(page, refs, flags); if (!folio)
@@ -2985,6 +2972,8 @@ static int gup_fast_pmd_leaf(pmd_t orig, pmd_t *pmdp, unsigned long addr, } *nr += refs; + for (; refs; refs--) + *(pages++) = page++; folio_set_referenced(folio); return 1; }
@@ -3003,8 +2992,8 @@ static int gup_fast_pud_leaf(pud_t orig, pud_t *pudp, unsigned long addr, if (pud_special(orig)) return 0; - page = pud_page(orig); - refs = record_subpages(page, PUD_SIZE, addr, end, pages + *nr); + refs = (end - addr) >> PAGE_SHIFT; + page = pud_page(orig) + ((addr & ~PUD_MASK) >> PAGE_SHIFT); folio = try_grab_folio_fast(page, refs, flags); if (!folio)
@@ -3026,6 +3015,8 @@ static int gup_fast_pud_leaf(pud_t orig, pud_t *pudp, unsigned long addr, } *nr += refs; + for (; refs; refs--) + *(pages++) = page++; folio_set_referenced(folio); return 1; }
--
2.50.1
--
Cheers
David / dhildenb