On Fri, Jul 27, 2012 at 5:43 AM, Cliff Wickman <cpw@xxxxxxx> wrote:
> From: Cliff Wickman <cpw@xxxxxxx>
>
> Gentlemen,
> I see that you all have done maintenance on mm/hugetlb.c, so I'm hoping one
> or two of you could comment on a problem and proposed fix.
>
>
> I am seeing list corruption occurring from within gather_surplus_pages()
> (mm/hugetlb.c). The problem occurs under a heavy load, and seems to be
> because this function drops the hugetlb_lock.
>
> I have CONFIG_DEBUG_LIST=y, and am running an MPI application with 64 threads
> and a library that creates a large heap of hugetlbfs pages for it.
>
> The below patch fixes the problem.
> The gist of this patch is that gather_surplus_pages() does not have to drop
> the lock if alloc_buddy_huge_page() is told whether the lock is already held.
>
> But I may be missing some reason why gather_surplus_pages() is unlocking and
> locking the hugetlb_lock several times (besides around the allocator).
>
> Could you take a look and advise?
>
> Signed-off-by: Cliff Wickman <cpw@xxxxxxx>
> ---
> mm/hugetlb.c | 28 +++++++++++++++++-----------
> 1 file changed, 17 insertions(+), 11 deletions(-)
>
> Index: linux/mm/hugetlb.c
> ===================================================================
> --- linux.orig/mm/hugetlb.c
> +++ linux/mm/hugetlb.c
> @@ -747,7 +747,9 @@ static int free_pool_huge_page(struct hs
> return ret;
> }
>
> -static struct page *alloc_buddy_huge_page(struct hstate *h, int nid)
> +/* already_locked means the caller has already locked hugetlb_lock */
> +static struct page *alloc_buddy_huge_page(struct hstate *h, int nid,
> + int already_locked)
> {
> struct page *page;
> unsigned int r_nid;
> @@ -778,7 +780,8 @@ static struct page *alloc_buddy_huge_pag
> * the node values until we've gotten the hugepage and only the
> * per-node value is checked there.
> */
> - spin_lock(&hugetlb_lock);
> + if (!already_locked)
> + spin_lock(&hugetlb_lock);
> if (h->surplus_huge_pages >= h->nr_overcommit_huge_pages) {
> spin_unlock(&hugetlb_lock);
> return NULL;
> @@ -787,6 +790,7 @@ static struct page *alloc_buddy_huge_pag
> h->surplus_huge_pages++;
> }
> spin_unlock(&hugetlb_lock);
> + /* page allocation may sleep, so the lock must be unlocked */
>
> if (nid == NUMA_NO_NODE)
> page = alloc_pages(htlb_alloc_mask|__GFP_COMP|
> @@ -799,6 +803,9 @@ static struct page *alloc_buddy_huge_pag
>
> if (page && arch_prepare_hugepage(page)) {
> __free_pages(page, huge_page_order(h));
> + if (already_locked)
> + /* leave it like it was */
> + spin_lock(&hugetlb_lock);
> return NULL;
> }
>
> @@ -817,7 +824,9 @@ static struct page *alloc_buddy_huge_pag
> h->surplus_huge_pages--;
> __count_vm_event(HTLB_BUDDY_PGALLOC_FAIL);
> }
> - spin_unlock(&hugetlb_lock);
> + if (!already_locked)
> + /* leave it like it was */
Same comment for two different checks?
> + spin_unlock(&hugetlb_lock);
>
> return page;
> }
> @@ -836,7 +845,7 @@ struct page *alloc_huge_page_node(struct
> spin_unlock(&hugetlb_lock);
>
> if (!page)
> - page = alloc_buddy_huge_page(h, nid);
> + page = alloc_buddy_huge_page(h, nid, 0);
>
> return page;
> }
> @@ -844,6 +853,7 @@ struct page *alloc_huge_page_node(struct
> /*
> * Increase the hugetlb pool such that it can accomodate a reservation
> * of size 'delta'.
> + * This is entered and exited with hugetlb_lock locked.
> */
> static int gather_surplus_pages(struct hstate *h, int delta)
> {
> @@ -863,9 +873,8 @@ static int gather_surplus_pages(struct h
>
> ret = -ENOMEM;
> retry:
> - spin_unlock(&hugetlb_lock);
> for (i = 0; i < needed; i++) {
> - page = alloc_buddy_huge_page(h, NUMA_NO_NODE);
> + page = alloc_buddy_huge_page(h, NUMA_NO_NODE, 1);
> if (!page)
> /*
> * We were not able to allocate enough pages to
Hm, what tree are you using(next tree please if not)?
Good Weekend
Hillf
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