Re: [PATCH] mm: introduce ARCH_PAGE_TABLE_SYNC_MASK_VMALLOC to sync kernel mapping conditionally
From: Harry Yoo <hidden>
Date: 2025-09-17 16:42:40
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linux-mm, lkml
On Wed, Sep 17, 2025 at 11:48:29PM +0800, alexjlzheng@gmail.com wrote:
From: Jinliang Zheng <redacted>
After commit 6eb82f994026 ("x86/mm: Pre-allocate P4D/PUD pages for
vmalloc area"), we don't need to synchronize kernel mappings in the
vmalloc area on x86_64.Right.
And commit 58a18fe95e83 ("x86/mm/64: Do not sync vmalloc/ioremap
mappings") actually does this.Right.
But commit 6659d0279980 ("x86/mm/64: define ARCH_PAGE_TABLE_SYNC_MASK
and arch_sync_kernel_mappings()") breaks this.Good point.
This patch introduces ARCH_PAGE_TABLE_SYNC_MASK_VMALLOC to avoid
unnecessary kernel mappings synchronization of the vmalloc area.
Fixes: 6659d0279980 ("x86/mm/64: define ARCH_PAGE_TABLE_SYNC_MASK and arch_sync_kernel_mappings()")The commit is getting backported to -stable kernels. Do you think this can cause a visible performance regression from user point of view, or it's just a nice optimization to have? (and any data to support?)
quoted hunk ↗ jump to hunk
Signed-off-by: Jinliang Zheng <redacted> --- arch/arm/include/asm/page.h | 3 ++- arch/x86/include/asm/pgtable-2level_types.h | 3 ++- arch/x86/include/asm/pgtable-3level_types.h | 3 ++- include/linux/pgtable.h | 4 ++++ mm/memory.c | 2 +- mm/vmalloc.c | 6 +++--- 6 files changed, 14 insertions(+), 7 deletions(-)diff --git a/mm/memory.c b/mm/memory.c index 0ba4f6b71847..cd2488043f8f 100644 --- a/mm/memory.c +++ b/mm/memory.c@@ -3170,7 +3170,7 @@ static int __apply_to_page_range(struct mm_struct *mm, unsigned long addr, break; } while (pgd++, addr = next, addr != end); - if (mask & ARCH_PAGE_TABLE_SYNC_MASK) + if (mask & ARCH_PAGE_TABLE_SYNC_MASK_VMALLOC) arch_sync_kernel_mappings(start, start + size);
But vmalloc is not the only user of apply_to_page_range()? -- Cheers, Harry / Hyeonggon