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authorGleb Natapov <gleb@redhat.com>2011-03-22 16:30:51 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2011-03-22 17:44:02 -0700
commit318b275fbca1ab9ec0862de71420e0e92c3d1aa7 (patch)
treeaa4984469443ed53b4e7fa23d3f91966e536a803 /mm/memory.c
parent5fda1bd5b8869574dad8e1f9f71e23bf0c186274 (diff)
mm: allow GUP to fail instead of waiting on a page
GUP user may want to try to acquire a reference to a page if it is already in memory, but not if IO, to bring it in, is needed. For example KVM may tell vcpu to schedule another guest process if current one is trying to access swapped out page. Meanwhile, the page will be swapped in and the guest process, that depends on it, will be able to run again. This patch adds FAULT_FLAG_RETRY_NOWAIT (suggested by Linus) and FOLL_NOWAIT follow_page flags. FAULT_FLAG_RETRY_NOWAIT, when used in conjunction with VM_FAULT_ALLOW_RETRY, indicates to handle_mm_fault that it shouldn't drop mmap_sem and wait on a page, but return VM_FAULT_RETRY instead. [akpm@linux-foundation.org: improve FOLL_NOWAIT comment] Signed-off-by: Gleb Natapov <gleb@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Hugh Dickins <hughd@google.com> Acked-by: Rik van Riel <riel@redhat.com> Cc: Michel Lespinasse <walken@google.com> Cc: Avi Kivity <avi@redhat.com> Cc: Marcelo Tosatti <mtosatti@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/memory.c')
-rw-r--r--mm/memory.c5
1 files changed, 4 insertions, 1 deletions
diff --git a/mm/memory.c b/mm/memory.c
index e48945ab362b..615be5127ce1 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1569,6 +1569,8 @@ int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
fault_flags |= FAULT_FLAG_WRITE;
if (nonblocking)
fault_flags |= FAULT_FLAG_ALLOW_RETRY;
+ if (foll_flags & FOLL_NOWAIT)
+ fault_flags |= (FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT);
ret = handle_mm_fault(mm, vma, start,
fault_flags);
@@ -1595,7 +1597,8 @@ int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
tsk->min_flt++;
if (ret & VM_FAULT_RETRY) {
- *nonblocking = 0;
+ if (nonblocking)
+ *nonblocking = 0;
return i;
}