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authorJoonsoo Kim <iamjoonsoo.kim@lge.com>2013-09-11 14:21:18 -0700
committerSteve Capper <steve.capper@linaro.org>2014-06-12 08:48:11 +0100
commit46e6f80655a62bd6fc00a0fbd03b244a50b0b247 (patch)
treec55a7c24c48fec450777968fd7d07ac586d31716
parent9ce28210c5fddd88e5c92dcacafbea649d996bec (diff)
downloadlinux-46e6f80655a62bd6fc00a0fbd03b244a50b0b247.tar.gz
mm, hugetlb: decrement reserve count if VM_NORESERVE alloc page cache
If a vma with VM_NORESERVE allocate a new page for page cache, we should check whether this area is reserved or not. If this address is already reserved by other process(in case of chg == 0), we should decrement reserve count, because this allocated page will go into page cache and currently, there is no way to know that this page comes from reserved pool or not when releasing inode. This may introduce over-counting problem to reserved count. With following example code, you can easily reproduce this situation. Assume 2MB, nr_hugepages = 100 size = 20 * MB; flag = MAP_SHARED; p = mmap(NULL, size, PROT_READ|PROT_WRITE, flag, fd, 0); if (p == MAP_FAILED) { fprintf(stderr, "mmap() failed: %s\n", strerror(errno)); return -1; } flag = MAP_SHARED | MAP_NORESERVE; q = mmap(NULL, size, PROT_READ|PROT_WRITE, flag, fd, 0); if (q == MAP_FAILED) { fprintf(stderr, "mmap() failed: %s\n", strerror(errno)); } q[0] = 'c'; After finish the program, run 'cat /proc/meminfo'. You can see below result. HugePages_Free: 100 HugePages_Rsvd: 1 To fix this, we should check our mapping type and tracked region. If our mapping is VM_NORESERVE, VM_MAYSHARE and chg is 0, this imply that current allocated page will go into page cache which is already reserved region when mapping is created. In this case, we should decrease reserve count. As implementing above, this patch solve the problem. [akpm@linux-foundation.org: fix spelling in comment] Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com> Reviewed-by: Wanpeng Li <liwanp@linux.vnet.ibm.com> Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com> Acked-by: Hillf Danton <dhillf@gmail.com> Acked-by: Michal Hocko <mhocko@suse.cz> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Cc: Rik van Riel <riel@redhat.com> Cc: Mel Gorman <mgorman@suse.de> Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Hugh Dickins <hughd@google.com> Cc: Davidlohr Bueso <davidlohr.bueso@hp.com> Cc: David Gibson <david@gibson.dropbear.id.au> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/hugetlb.c34
1 files changed, 26 insertions, 8 deletions
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 84a77f0f89f..fd1cb472a2b 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -444,10 +444,23 @@ void reset_vma_resv_huge_pages(struct vm_area_struct *vma)
}
/* Returns true if the VMA has associated reserve pages */
-static int vma_has_reserves(struct vm_area_struct *vma)
+static int vma_has_reserves(struct vm_area_struct *vma, long chg)
{
- if (vma->vm_flags & VM_NORESERVE)
- return 0;
+ if (vma->vm_flags & VM_NORESERVE) {
+ /*
+ * This address is already reserved by other process(chg == 0),
+ * so, we should decrement reserved count. Without decrementing,
+ * reserve count remains after releasing inode, because this
+ * allocated page will go into page cache and is regarded as
+ * coming from reserved pool in releasing step. Currently, we
+ * don't have any other solution to deal with this situation
+ * properly, so add work-around here.
+ */
+ if (vma->vm_flags & VM_MAYSHARE && chg == 0)
+ return 1;
+ else
+ return 0;
+ }
/* Shared mappings always use reserves */
if (vma->vm_flags & VM_MAYSHARE)
@@ -527,7 +540,8 @@ static struct page *dequeue_huge_page_node(struct hstate *h, int nid)
static struct page *dequeue_huge_page_vma(struct hstate *h,
struct vm_area_struct *vma,
- unsigned long address, int avoid_reserve)
+ unsigned long address, int avoid_reserve,
+ long chg)
{
struct page *page = NULL;
struct mempolicy *mpol;
@@ -546,7 +560,7 @@ retry_cpuset:
* have no page reserves. This check ensures that reservations are
* not "stolen". The child may still get SIGKILLed
*/
- if (!vma_has_reserves(vma) &&
+ if (!vma_has_reserves(vma, chg) &&
h->free_huge_pages - h->resv_huge_pages == 0)
goto err;
@@ -559,8 +573,12 @@ retry_cpuset:
if (cpuset_zone_allowed_softwall(zone, htlb_alloc_mask)) {
page = dequeue_huge_page_node(h, zone_to_nid(zone));
if (page) {
- if (!avoid_reserve && vma_has_reserves(vma))
- h->resv_huge_pages--;
+ if (avoid_reserve)
+ break;
+ if (!vma_has_reserves(vma, chg))
+ break;
+
+ h->resv_huge_pages--;
break;
}
}
@@ -1180,7 +1198,7 @@ static struct page *alloc_huge_page(struct vm_area_struct *vma,
return ERR_PTR(-ENOSPC);
}
spin_lock(&hugetlb_lock);
- page = dequeue_huge_page_vma(h, vma, addr, avoid_reserve);
+ page = dequeue_huge_page_vma(h, vma, addr, avoid_reserve, chg);
if (!page) {
spin_unlock(&hugetlb_lock);
page = alloc_buddy_huge_page(h, NUMA_NO_NODE);