Re: [PATCH v3 4/6] mm/vmalloc: make set_area_direct_map HUGE_VMAP friendly
From: Dev Jain <dev.jain@arm.com>
Date: 2026-09-08 09:59:44
Also in:
linux-mm, linux-pm, linux-riscv, linux-s390, lkml, loongarch
On 03/09/26 2:58 pm, Mike Rapoport (Microsoft) wrote:
set_area_direct_map() always updates direct map alias permissions in single page increments. For HUGE_VMAP areas it's suboptimal. Not only the loop in set_area_direct_map() needlessly has more iterations (e.g times 512 on x86), but it also causes fragmentation of the direct map that could be avoided for the HUGE_VMAP areas populated with large pages.
Correct, this would also help us on arm64 once we have ROX caches.
All pages in an area are always of the same order: either same-order
large pages when VM_ALLOW_HUGE_VMAP is set and all huge pages were
successfully allocated, or order-0 page when VM_ALLOW_HUGE_VMAP is
cleared or when huge pages allocation fails and fallback path is taken.
Instead of updating the direct map permissions for every order-0 page in
an area, use the area's page_order as the loop increment and update the
large pages in one call to set_direct_map_{invalid,default}_noflush().
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
---LGTM: Reviewed-by: Dev Jain <dev.jain@arm.com>
quoted hunk ↗ jump to hunk
mm/vmalloc.c | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-)diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 5506b180f5c27..6ed6c160abed7 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c@@ -3367,12 +3367,15 @@ static inline void set_area_direct_map(const struct vm_struct *area, int (*set_direct_map)(struct page *page, unsigned int nr)) { - unsigned long i; + unsigned int nr = (1U << vm_area_page_order(area)); + + for (unsigned long i = 0; i < area->nr_pages; i += nr) { + if (page_address(area->pages[i])) { + int err = set_direct_map(area->pages[i], nr); - /* HUGE_VMALLOC passes small pages to set_direct_map */ - for (i = 0; i < area->nr_pages; i++) - if (page_address(area->pages[i])) - set_direct_map(area->pages[i], 1); + WARN_ON_ONCE(err); + } + } } /*