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From: Vlastimil Babka <vbabka@suse.cz>
To: Nikita <sh1r4s3@mail.si-head.nl>, linux-mm@kvack.org
Cc: Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH] mm/msync: exit early when the flags is an MS_ASYNC and start < vm_start
Date: Tue, 20 Oct 2020 17:03:56 +0200	[thread overview]
Message-ID: <75def548-28a2-729a-96b7-56ba91bfc94c@suse.cz> (raw)
In-Reply-To: <92411D90-AD5D-44B9-8F52-C2FA222BB4EB@mail.si-head.nl>

On 10/20/20 4:38 PM, Nikita wrote:
> Hi!
> 
>> On 20 Oct 2020, at 13:19, Vlastimil Babka <vbabka@suse.cz> 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@mail.si-head.nl>
>> 
>> 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
>> 
> 



  reply	other threads:[~2020-10-20 15:04 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-12 16:09 Nikita Ermakov
2020-10-20 10:19 ` Vlastimil Babka
2020-10-20 14:38   ` Nikita
2020-10-20 15:03     ` Vlastimil Babka [this message]
2020-10-20 16:19       ` Nikita
2020-10-20 20:56         ` [PATCH v2] " Nikita Ermakov
2020-10-23 11:12           ` Vlastimil Babka
2020-10-25  9:29             ` [PATCH v3] " Nikita Ermakov
2020-10-25  9:38             ` [PATCH v2] " Nikita Ermakov

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