memcgroup: reinstate swapoff mod
This patch reinstates the "swapoff: scan ptes preemptibly" mod we started
with: in due course it should be rendered down into the earlier patches,
leaving us with a more straightforward mem_cgroup_charge mod to unuse_pte,
allocating with GFP_KERNEL while holding no spinlock and no atomic kmap.
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Cc: Pavel Emelianov <xemul@openvz.org>
Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Paul Menage <menage@google.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Kirill Korotaev <dev@sw.ru>
Cc: Herbert Poetzl <herbert@13thfloor.at>
Cc: David Rientjes <rientjes@google.com>
Cc: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 35e00c3..02ccab5 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -507,11 +507,23 @@
* just let do_wp_page work it out if a write is requested later - to
* force COW, vm_page_prot omits write permission from any private vma.
*/
-static int unuse_pte(struct vm_area_struct *vma, pte_t *pte,
+static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
unsigned long addr, swp_entry_t entry, struct page *page)
{
+ spinlock_t *ptl;
+ pte_t *pte;
+ int ret = 1;
+
if (mem_cgroup_charge(page, vma->vm_mm, GFP_KERNEL))
- return -ENOMEM;
+ ret = -ENOMEM;
+
+ pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
+ if (unlikely(!pte_same(*pte, swp_entry_to_pte(entry)))) {
+ if (ret > 0)
+ mem_cgroup_uncharge_page(page);
+ ret = 0;
+ goto out;
+ }
inc_mm_counter(vma->vm_mm, anon_rss);
get_page(page);
@@ -524,7 +536,9 @@
* immediately swapped out again after swapon.
*/
activate_page(page);
- return 1;
+out:
+ pte_unmap_unlock(pte, ptl);
+ return ret;
}
static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
@@ -533,21 +547,33 @@
{
pte_t swp_pte = swp_entry_to_pte(entry);
pte_t *pte;
- spinlock_t *ptl;
int ret = 0;
- pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
+ /*
+ * We don't actually need pte lock while scanning for swp_pte: since
+ * we hold page lock and mmap_sem, swp_pte cannot be inserted into the
+ * page table while we're scanning; though it could get zapped, and on
+ * some architectures (e.g. x86_32 with PAE) we might catch a glimpse
+ * of unmatched parts which look like swp_pte, so unuse_pte must
+ * recheck under pte lock. Scanning without pte lock lets it be
+ * preemptible whenever CONFIG_PREEMPT but not CONFIG_HIGHPTE.
+ */
+ pte = pte_offset_map(pmd, addr);
do {
/*
* swapoff spends a _lot_ of time in this loop!
* Test inline before going to call unuse_pte.
*/
if (unlikely(pte_same(*pte, swp_pte))) {
- ret = unuse_pte(vma, pte++, addr, entry, page);
- break;
+ pte_unmap(pte);
+ ret = unuse_pte(vma, pmd, addr, entry, page);
+ if (ret)
+ goto out;
+ pte = pte_offset_map(pmd, addr);
}
} while (pte++, addr += PAGE_SIZE, addr != end);
- pte_unmap_unlock(pte - 1, ptl);
+ pte_unmap(pte - 1);
+out:
return ret;
}