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Message-ID: <7e184caf-2447-48d4-8d7c-1b63deb0f418@arm.com>
Date: Mon, 10 Feb 2025 12:41:13 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: Ryan Roberts <ryan.roberts@....com>,
Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
Muchun Song <muchun.song@...ux.dev>,
Pasha Tatashin <pasha.tatashin@...een.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Uladzislau Rezki <urezki@...il.com>, Christoph Hellwig <hch@...radead.org>,
Mark Rutland <mark.rutland@....com>, Ard Biesheuvel <ardb@...nel.org>,
Dev Jain <dev.jain@....com>, Alexandre Ghiti <alexghiti@...osinc.com>,
Steve Capper <steve.capper@...aro.org>, Kevin Brodsky <kevin.brodsky@....com>
Cc: linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 14/16] mm/vmalloc: Batch arch_sync_kernel_mappings()
more efficiently
On 2/5/25 20:39, Ryan Roberts wrote:
> When page_shift is greater than PAGE_SIZE, __vmap_pages_range_noflush()
> will call vmap_range_noflush() for each individual huge page. But
> vmap_range_noflush() would previously call arch_sync_kernel_mappings()
> directly so this would end up being called for every huge page.
>
> We can do better than this; refactor the call into the outer
> __vmap_pages_range_noflush() so that it is only called once for the
> entire batch operation.
This makes sense.
>
> This will benefit performance for arm64 which is about to opt-in to
> using the hook.
>
> Signed-off-by: Ryan Roberts <ryan.roberts@....com>
> ---
> mm/vmalloc.c | 60 ++++++++++++++++++++++++++--------------------------
> 1 file changed, 30 insertions(+), 30 deletions(-)
>
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 68950b1824d0..50fd44439875 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -285,40 +285,38 @@ static int vmap_p4d_range(pgd_t *pgd, unsigned long addr, unsigned long end,
>
> static int vmap_range_noflush(unsigned long addr, unsigned long end,
> phys_addr_t phys_addr, pgprot_t prot,
> - unsigned int max_page_shift)
> + unsigned int max_page_shift, pgtbl_mod_mask *mask)
> {
> pgd_t *pgd;
> - unsigned long start;
> unsigned long next;
> int err;
> - pgtbl_mod_mask mask = 0;
>
> might_sleep();
> BUG_ON(addr >= end);
>
> - start = addr;
> pgd = pgd_offset_k(addr);
> do {
> next = pgd_addr_end(addr, end);
> err = vmap_p4d_range(pgd, addr, next, phys_addr, prot,
> - max_page_shift, &mask);
> + max_page_shift, mask);
> if (err)
> break;
> } while (pgd++, phys_addr += (next - addr), addr = next, addr != end);
>
> - if (mask & ARCH_PAGE_TABLE_SYNC_MASK)
> - arch_sync_kernel_mappings(start, end);
> -
> return err;
> }
arch_sync_kernel_mappings() gets dropped here and moved to existing
vmap_range_noflush() callers instead.
>
> int vmap_page_range(unsigned long addr, unsigned long end,
> phys_addr_t phys_addr, pgprot_t prot)
> {
> + pgtbl_mod_mask mask = 0;
> int err;
>
> err = vmap_range_noflush(addr, end, phys_addr, pgprot_nx(prot),
> - ioremap_max_page_shift);
> + ioremap_max_page_shift, &mask);
> + if (mask & ARCH_PAGE_TABLE_SYNC_MASK)
> + arch_sync_kernel_mappings(addr, end);
> +
arch_sync_kernel_mappings() gets moved here.
> flush_cache_vmap(addr, end);
> if (!err)
> err = kmsan_ioremap_page_range(addr, end, phys_addr, prot,
> @@ -587,29 +585,24 @@ static int vmap_pages_p4d_range(pgd_t *pgd, unsigned long addr,
> }
>
> static int vmap_small_pages_range_noflush(unsigned long addr, unsigned long end,
> - pgprot_t prot, struct page **pages)
> + pgprot_t prot, struct page **pages, pgtbl_mod_mask *mask)
> {
> - unsigned long start = addr;
> pgd_t *pgd;
> unsigned long next;
> int err = 0;
> int nr = 0;
> - pgtbl_mod_mask mask = 0;
>
> BUG_ON(addr >= end);
> pgd = pgd_offset_k(addr);
> do {
> next = pgd_addr_end(addr, end);
> if (pgd_bad(*pgd))
> - mask |= PGTBL_PGD_MODIFIED;
> - err = vmap_pages_p4d_range(pgd, addr, next, prot, pages, &nr, &mask);
> + *mask |= PGTBL_PGD_MODIFIED;
> + err = vmap_pages_p4d_range(pgd, addr, next, prot, pages, &nr, mask);
> if (err)
> break;
> } while (pgd++, addr = next, addr != end);
>
> - if (mask & ARCH_PAGE_TABLE_SYNC_MASK)
> - arch_sync_kernel_mappings(start, end);
> -
> return err;
> }
>
> @@ -626,26 +619,33 @@ int __vmap_pages_range_noflush(unsigned long addr, unsigned long end,
> pgprot_t prot, struct page **pages, unsigned int page_shift)
> {
> unsigned int i, nr = (end - addr) >> PAGE_SHIFT;
> + unsigned long start = addr;
> + pgtbl_mod_mask mask = 0;
> + int err = 0;
>
> WARN_ON(page_shift < PAGE_SHIFT);
>
> if (!IS_ENABLED(CONFIG_HAVE_ARCH_HUGE_VMALLOC) ||
> - page_shift == PAGE_SHIFT)
> - return vmap_small_pages_range_noflush(addr, end, prot, pages);
> -
> - for (i = 0; i < nr; i += 1U << (page_shift - PAGE_SHIFT)) {
> - int err;
> -
> - err = vmap_range_noflush(addr, addr + (1UL << page_shift),
> - page_to_phys(pages[i]), prot,
> - page_shift);
> - if (err)
> - return err;
> + page_shift == PAGE_SHIFT) {
> + err = vmap_small_pages_range_noflush(addr, end, prot, pages,
> + &mask);
Unlike earlier don't return here until arch_sync_kernel_mappings()
gets covered later.
> + } else {
> + for (i = 0; i < nr; i += 1U << (page_shift - PAGE_SHIFT)) {
> + err = vmap_range_noflush(addr,
> + addr + (1UL << page_shift),
> + page_to_phys(pages[i]), prot,
> + page_shift, &mask);
> + if (err)
> + break;
>
> - addr += 1UL << page_shift;
> + addr += 1UL << page_shift;
> + }
> }
>
> - return 0;
> + if (mask & ARCH_PAGE_TABLE_SYNC_MASK)
> + arch_sync_kernel_mappings(start, end);
arch_sync_kernel_mappings() gets moved here after getting dropped
from both vmap_range_noflush() and vmap_small_pages_range_noflush().
> +
> + return err;
> }
>
> int vmap_pages_range_noflush(unsigned long addr, unsigned long end,
LGTM, and this can stand on its own as well.
Reviewed-by: Anshuman Khandual <anshuman.khandual@....com>
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