On Sat, Nov 22, 2025 at 05:03:43PM +0800, Barry Song wrote:
From: Barry Song v-songbaohua@oppo.com
In many cases, the pages passed to vmap() may include high-order pages—for example, the systemheap often allocates pages in descending order: order 8, then 4, then 0. Currently, vmap() iterates over every page individually—even the pages inside a high-order block are handled one by one. This patch detects high-order pages and maps them as a single contiguous block whenever possible.
Another possibility is to implement a new API, vmap_sg(). However, that change seems to be quite large in scope.
When vmapping a 128MB dma-buf using the systemheap, this RFC appears to make system_heap_do_vmap() 16× faster:
W/ patch: [ 51.363682] system_heap_do_vmap took 2474000 ns [ 53.307044] system_heap_do_vmap took 2469008 ns [ 55.061985] system_heap_do_vmap took 2519008 ns [ 56.653810] system_heap_do_vmap took 2674000 ns
W/o patch: [ 8.260880] system_heap_do_vmap took 39490000 ns [ 32.513292] system_heap_do_vmap took 38784000 ns [ 82.673374] system_heap_do_vmap took 40711008 ns [ 84.579062] system_heap_do_vmap took 40236000 ns
Cc: Uladzislau Rezki urezki@gmail.com Cc: Sumit Semwal sumit.semwal@linaro.org Cc: John Stultz jstultz@google.com Cc: Maxime Ripard mripard@kernel.org Signed-off-by: Barry Song v-songbaohua@oppo.com
mm/vmalloc.c | 49 +++++++++++++++++++++++++++++++++++++++++++------ 1 file changed, 43 insertions(+), 6 deletions(-)
diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 0832f944544c..af2e3e8c052a 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -642,6 +642,34 @@ static int vmap_small_pages_range_noflush(unsigned long addr, unsigned long end, return err; } +static inline int get_vmap_batch_order(struct page **pages,
unsigned int stride,int max_steps,unsigned int idx)+{
- /*
* Currently, batching is only supported in vmap_pages_range* when page_shift == PAGE_SHIFT.*/- if (stride != 1)
return 0;- struct page *base = pages[idx];
- if (!PageHead(base))
return 0;- int order = compound_order(base);
- int nr_pages = 1 << order;
- if (max_steps < nr_pages)
return 0;- for (int i = 0; i < nr_pages; i++)
if (pages[idx + i] != base + i)return 0;- return order;
+}
/*
- vmap_pages_range_noflush is similar to vmap_pages_range, but does not
- flush caches.
@@ -655,23 +683,32 @@ 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 int stride;
WARN_ON(page_shift < PAGE_SHIFT);
- /*
* Some users may allocate pages from high-order down to order 0.* We roughly check if the first page is a compound page. If so,* there is a chance to batch multiple pages together.*/
page_shift == PAGE_SHIFT)
(page_shift == PAGE_SHIFT && !PageCompound(pages[0])))
Do we support __GFP_COMP as vmalloc/vmap flag? As i see from latest:
/* * See __vmalloc_node_range() for a clear list of supported vmalloc flags. * This gfp lists all flags currently passed through vmalloc. Currently, * __GFP_ZERO is used by BPF and __GFP_NORETRY is used by percpu. Both drm * and BPF also use GFP_USER. Additionally, various users pass * GFP_KERNEL_ACCOUNT. Xfs uses __GFP_NOLOCKDEP. */ #define GFP_VMALLOC_SUPPORTED (GFP_KERNEL | GFP_ATOMIC | GFP_NOWAIT |\ __GFP_NOFAIL | __GFP_ZERO | __GFP_NORETRY |\ GFP_NOFS | GFP_NOIO | GFP_KERNEL_ACCOUNT |\ GFP_USER | __GFP_NOLOCKDEP)
Could you please clarify when PageCompound(pages[0]) returns true?
return vmap_small_pages_range_noflush(addr, end, prot, pages);
- for (i = 0; i < nr; i += 1U << (page_shift - PAGE_SHIFT)) {
int err;
- stride = 1U << (page_shift - PAGE_SHIFT);
- for (i = 0; i < nr; ) {
int err, order;
err = vmap_range_noflush(addr, addr + (1UL << page_shift),
order = get_vmap_batch_order(pages, stride, nr - i, i);err = vmap_range_noflush(addr, addr + (1UL << (page_shift + order)), page_to_phys(pages[i]), prot,
page_shift);
page_shift + order);
addr += 1UL << page_shift;
addr += 1UL << (page_shift + order);i += 1U << (order + page_shift - PAGE_SHIFT);return 0; -- 2.39.3 (Apple Git-146)