On Mon, 2016-11-21 at 01:35 +0000, Al Viro wrote:
>
> Umm... One possibility would be something like fs/namespace.c:m_start() -
> if nothing has changed since the last time, just use a cached pointer.
> That has sped the damn thing (/proc/mounts et.al.) big way, but it's
> dependent upon having an event count updated whenever we change the
> mount tree - doing the same for vma_area list might or might not be
> a good idea. /proc/mounts and friends get ->poll() on that as well;
> that probably would _not_ be a good idea in this case.
Yes, a generation number could help in some cases.
Another potential issue with CONFIG_VMAP_STACK is that we make no
attempt to allocate 4 consecutive pages.
Even if we have plenty of memory, 4 calls to alloc_page() are likely to
give us 4 pages in completely different locations.
Here I printed the hugepage number of the 4 pages for some stacks :
0xffffc9001a07c000-0xffffc9001a081000 20480 _do_fork+0xe1/0x360 pages=4
vmalloc Hfcac Hfeba Hfec0 Hfc9d N0=4
0xffffc9001a084000-0xffffc9001a089000 20480 _do_fork+0xe1/0x360 pages=4
vmalloc Hfc79 Hfc79 Hfc79 Hfc83 N0=4
0xffffc9001a08c000-0xffffc9001a091000 20480 _do_fork+0xe1/0x360 pages=4
vmalloc Hfc9b Hfe91 Hfebe Hfca2 N0=4
0xffffc9001a094000-0xffffc9001a099000 20480 _do_fork+0xe1/0x360 pages=4
vmalloc Hfcaa Hfcaa Hfca6 Hfebc N0=4
0xffffc9001a09c000-0xffffc9001a0a1000 20480 _do_fork+0xe1/0x360 pages=4
vmalloc Hfe9b Hfe90 Hff09 Hfefb N0=4
0xffffc9001a0a4000-0xffffc9001a0a9000 20480 _do_fork+0xe1/0x360 pages=4
vmalloc Hfe94 Hfe62 Hfea0 Hfe7b N0=4
0xffffc9001a0ac000-0xffffc9001a0b1000 20480 _do_fork+0xe1/0x360 pages=4
vmalloc Hfe78 Hff05 Hff05 Hfc74 N0=4
0xffffc9001a0b4000-0xffffc9001a0b9000 20480 _do_fork+0xe1/0x360 pages=4
vmalloc Hfc9b Hfc9b Hfe83 Hf782 N0=4
0xffffc9001a0bc000-0xffffc9001a0c1000 20480 _do_fork+0xe1/0x360 pages=4
vmalloc Hfe78 Hfe78 Hfc7f Hfc7f N0=4
0xffffc9001a0c4000-0xffffc9001a0c9000 20480 _do_fork+0xe1/0x360 pages=4
vmalloc Hfebe Hfebe Hfe82 Hfe85 N0=4
0xffffc9001a0cc000-0xffffc9001a0d1000 20480 _do_fork+0xe1/0x360 pages=4
vmalloc Hfc6b Hfe62 Hfe62 Hfcaa N0=4
0xffffc9001a0d4000-0xffffc9001a0d9000 20480 _do_fork+0xe1/0x360 pages=4
vmalloc Hfebd Hfebd Hfc92 Hfc92 N0=4
This is a vmalloc() generic issue that is worth fixing now ?
Note this RFC might conflict with NUMA interleave policy.
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index f2481cb4e6b2..0123e97debb9 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -1602,9 +1602,10 @@ static void *__vmalloc_area_node(struct vm_struct *area,
gfp_t gfp_mask,
pgprot_t prot, int node)
{
struct page **pages;
- unsigned int nr_pages, array_size, i;
+ unsigned int nr_pages, array_size, i, j;
const gfp_t nested_gfp = (gfp_mask & GFP_RECLAIM_MASK) | __GFP_ZERO;
const gfp_t alloc_mask = gfp_mask | __GFP_NOWARN;
+ const gfp_t multi_alloc_mask = (gfp_mask & ~__GFP_DIRECT_RECLAIM) |
__GFP_NORETRY;
nr_pages = get_vm_area_size(area) >> PAGE_SHIFT;
array_size = (nr_pages * sizeof(struct page *));
@@ -1624,20 +1625,34 @@ static void *__vmalloc_area_node(struct vm_struct
*area, gfp_t gfp_mask,
return NULL;
}
- for (i = 0; i < area->nr_pages; i++) {
- struct page *page;
-
- if (node == NUMA_NO_NODE)
- page = alloc_page(alloc_mask);
- else
- page = alloc_pages_node(node, alloc_mask, 0);
+ for (i = 0; i < area->nr_pages;) {
+ struct page *page = NULL;
+ unsigned int chunk_order = min(ilog2(area->nr_pages - i),
MAX_ORDER - 1);
+
+ while (chunk_order && !page) {
+ if (node == NUMA_NO_NODE)
+ page = alloc_pages(multi_alloc_mask,
chunk_order);
+ else
+ page = alloc_pages_node(node, multi_alloc_mask,
chunk_order);
+ if (page)
+ split_page(page, chunk_order);
+ else
+ chunk_order--;
+ }
+ if (!page) {
+ if (node == NUMA_NO_NODE)
+ page = alloc_pages(alloc_mask, 0);
+ else
+ page = alloc_pages_node(node, alloc_mask, 0);
+ }
if (unlikely(!page)) {
/* Successfully allocated i pages, free them in
__vunmap() */
area->nr_pages = i;
goto fail;
}
- area->pages[i] = page;
+ for (j = 0; j < (1 << chunk_order); j++)
+ area->pages[i++] = page++;
if (gfpflags_allow_blocking(gfp_mask))
cond_resched();
}
