On 10/20/20 4:38 PM, Nikita wrote:
Hi!
On 20 Oct 2020, at 13:19, Vlastimil Babka <vbabka@xxxxxxx> wrote:
On 10/12/20 6:09 PM, Nikita Ermakov wrote:
Exit from the loop over the VMA in the case when the flags
contain only an MS_ASYNC and start < vm_start. In this case msync()
would return with -ENOMEM anyway so make it return early.
Signed-off-by: Nikita Ermakov <sh1r4s3@xxxxxxxxxxxxxxx>
AFAICS it can still return -EBUSY if there's MS_INVALIDATE and a mlocked vma. This is all subtle and I don't think we should risk breaking something for this optimization.
Yes, it could. But in this patch the optimization works only in the case if the flag is MS_ASYNC. If the flag is (MS_ASYNC | MS_INVALIDATE).
Ah, right, it compares "== MS_ASYNC" not "& MS_ASYNC" so it's correct. A comment
would be nice, such as:
We found an unmapped range and with MS_ASYNC and no MS_INVALIDATE there's
nothing to do and the result will always be -ENOMEM, so we can return immediately.
---
mm/msync.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/mm/msync.c b/mm/msync.c
index 69c6d2029531..ed20c3621d4c 100644
--- a/mm/msync.c
+++ b/mm/msync.c
@@ -69,6 +69,8 @@ SYSCALL_DEFINE3(msync, unsigned long, start, size_t, len, int, flags)
goto out_unlock;
/* Here start < vma->vm_end. */
if (start < vma->vm_start) {
+ if (flags == MS_ASYNC)
+ goto out_unlock;
start = vma->vm_start;
if (start >= end)
goto out_unlock;
base-commit: 6824a8a9b4861d7df7ee132a952bdf6f84a99cb8
