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authorHuang Ying <ying.huang@intel.com>2017-07-06 15:37:28 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2017-07-06 16:24:31 -0700
commitb8f593cd0896b8b14c2b494a9776531b5cd54d98 (patch)
tree5338b7e5f1c1dc5aefb2473e780c27179f4d97da /mm/huge_memory.c
parent0f0746589e4be071a8f890b2035c97c30c7a4e16 (diff)
downloadlinux-b8f593cd0896b8b14c2b494a9776531b5cd54d98.tar.bz2
mm, THP, swap: check whether THP can be split firstly
To swap out THP (Transparent Huage Page), before splitting the THP, the swap cluster will be allocated and the THP will be added into the swap cache. But it is possible that the THP cannot be split, so that we must delete the THP from the swap cache and free the swap cluster. To avoid that, in this patch, whether the THP can be split is checked firstly. The check can only be done racy, but it is good enough for most cases. With the patch, the swap out throughput improves 3.6% (from about 4.16GB/s to about 4.31GB/s) in the vm-scalability swap-w-seq test case with 8 processes. The test is done on a Xeon E5 v3 system. The swap device used is a RAM simulated PMEM (persistent memory) device. To test the sequential swapping out, the test case creates 8 processes, which sequentially allocate and write to the anonymous pages until the RAM and part of the swap device is used up. Link: http://lkml.kernel.org/r/20170515112522.32457-5-ying.huang@intel.com Signed-off-by: "Huang, Ying" <ying.huang@intel.com> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> [for can_split_huge_page()] Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Ebru Akagunduz <ebru.akagunduz@gmail.com> Cc: Hugh Dickins <hughd@google.com> Cc: Michal Hocko <mhocko@kernel.org> Cc: Minchan Kim <minchan@kernel.org> Cc: Rik van Riel <riel@redhat.com> Cc: Shaohua Li <shli@kernel.org> Cc: Tejun Heo <tj@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/huge_memory.c')
-rw-r--r--mm/huge_memory.c20
1 files changed, 16 insertions, 4 deletions
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 1a168e4bac4b..86975dec0ba1 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2390,6 +2390,21 @@ int page_trans_huge_mapcount(struct page *page, int *total_mapcount)
return ret;
}
+/* Racy check whether the huge page can be split */
+bool can_split_huge_page(struct page *page, int *pextra_pins)
+{
+ int extra_pins;
+
+ /* Additional pins from radix tree */
+ if (PageAnon(page))
+ extra_pins = PageSwapCache(page) ? HPAGE_PMD_NR : 0;
+ else
+ extra_pins = HPAGE_PMD_NR;
+ if (pextra_pins)
+ *pextra_pins = extra_pins;
+ return total_mapcount(page) == page_count(page) - extra_pins - 1;
+}
+
/*
* This function splits huge page into normal pages. @page can point to any
* subpage of huge page to split. Split doesn't change the position of @page.
@@ -2437,7 +2452,6 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
ret = -EBUSY;
goto out;
}
- extra_pins = PageSwapCache(page) ? HPAGE_PMD_NR : 0;
mapping = NULL;
anon_vma_lock_write(anon_vma);
} else {
@@ -2449,8 +2463,6 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
goto out;
}
- /* Addidional pins from radix tree */
- extra_pins = HPAGE_PMD_NR;
anon_vma = NULL;
i_mmap_lock_read(mapping);
}
@@ -2459,7 +2471,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
* Racy check if we can split the page, before freeze_page() will
* split PMDs
*/
- if (total_mapcount(head) != page_count(head) - extra_pins - 1) {
+ if (!can_split_huge_page(head, &extra_pins)) {
ret = -EBUSY;
goto out_unlock;
}