> On 20 Oct 2020, at 18:03, Vlastimil Babka <vbabka@xxxxxxx> wrote:
>
> 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.
>
Thanks for the comment!
I should probably implement this comment to the patch description and resubmit it as v2.
>>>> ---
>>>> 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
>
