On 11/22/25 10:03, 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)
These fit into less lines.
ideally
\t\tunsigned int stride, int max_steps, unsigned int idx)
+{
int order, nr_pages, i; struct page *base;
But I think you can just drop "base". And order.
- /*
* 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;
You can drop the head check etc and simply do
nr_pages = compound_nr(pages[idx]); if (nr_pages == 1) return 0;
Which raises the question: are these things folios? I assume not.
- if (max_steps < nr_pages)
return 0;- for (int i = 0; i < nr_pages; i++)
if (pages[idx + i] != base + i)return 0;
if (num_pages_contiguous(&pages[idx], nr_pages) == nr_pages) return compound_order(pages[idx]); return 0;