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From: Vlastimil Babka <vbabka@suse.cz>
To: mtk.manpages@gmail.com
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>,
	Dave Hansen <dave.hansen@intel.com>, Mel Gorman <mgorman@suse.de>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	Minchan Kim <minchan@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	lkml <linux-kernel@vger.kernel.org>,
	Linux API <linux-api@vger.kernel.org>,
	linux-man <linux-man@vger.kernel.org>,
	Hugh Dickins <hughd@google.com>
Subject: Re: MADV_DONTNEED semantics? Was: [RFC PATCH] mm: madvise: Ignore repeated MADV_DONTNEED hints
Date: Wed, 04 Feb 2015 18:02:02 +0100	[thread overview]
Message-ID: <54D2508A.9030804@suse.cz> (raw)
In-Reply-To: <CAKgNAkgOOCuzJz9whoVfFjqhxM0zYsz94B1+oH58SthC5Ut9sg@mail.gmail.com>

On 02/04/2015 03:00 PM, Michael Kerrisk (man-pages) wrote:
> Hello Vlastimil,
>
> On 4 February 2015 at 14:46, Vlastimil Babka <vbabka@suse.cz> wrote:
>>>> - that covers mlocking ok, not sure if the rest fits the "shared pages"
>>>> case
>>>> though. I dont see any check for other kinds of shared pages in the code.
>>>
>>> Agreed. "shared" here seems confused. I've removed it. And I've
>>> added mention of "Huge TLB pages" for this error.
>>
>> Thanks.
>
> I also added those cases for MADV_REMOVE, BTW.

Right. There's also the following for MADV_REMOVE that needs updating:

"Currently, only shmfs/tmpfs supports this; other filesystems return 
with the error ENOSYS."

- it's not just shmem/tmpfs anymore. It should be best to refer to 
fallocate(2) option FALLOC_FL_PUNCH_HOLE which seems to be (more) up to 
date.

- AFAICS it doesn't return ENOSYS but EOPNOTSUPP. Also neither error 
code is listed in the ERRORS section.

>>>>>> - The word "will result" did sound as a guarantee at least to me. So
>>>>>> here it
>>>>>> could be changed to "may result (unless the advice is ignored)"?
>>>>>
>>>>> It's too late to fix documentation. Applications already depends on the
>>>>> beheviour.
>>>>
>>>> Right, so as long as they check for EINVAL, it should be safe. It appears
>>>> that
>>>> jemalloc does.
>>>
>>>
>>> So, first a brief question: in the cases where the call does not error
>>> out,
>>> are we agreed that in the current implementation, MADV_DONTNEED will
>>> always result in zero-filled pages when the region is faulted back in
>>> (when we consider pages that are not backed by a file)?
>>
>>
>> I'd agree at this point.
>
> Thanks for the confirmation.
>
>> Also we should probably mention anonymously shared pages (shmem). I think
>> they behave the same as file here.
>
> You mean tmpfs here, right? (I don't keep all of the synonyms straight.)

shmem is tmpfs (that by itself would fit under "files" just fine), but 
also sys V segments created by shmget(2) and also mappings created by 
mmap with MAP_SHARED | MAP_ANONYMOUS. I'm not sure if there's a single 
manpage to refer to the full list.

Thanks,
Vlastimil

  reply	other threads:[~2015-02-04 17:02 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-02-02 16:55 Mel Gorman
2015-02-02 22:05 ` Andrew Morton
2015-02-02 22:18   ` Mel Gorman
2015-02-02 22:35     ` Andrew Morton
2015-02-03  0:26       ` Davidlohr Bueso
2015-02-03 10:50       ` Mel Gorman
2015-02-05 21:44     ` Rik van Riel
2015-02-02 22:22 ` Dave Hansen
2015-02-03  8:19   ` MADV_DONTNEED semantics? Was: " Vlastimil Babka
2015-02-03 10:53     ` Kirill A. Shutemov
2015-02-03 11:42       ` Vlastimil Babka
2015-02-03 16:20         ` Michael Kerrisk (man-pages)
2015-02-04 13:46           ` Vlastimil Babka
2015-02-04 14:00             ` Michael Kerrisk (man-pages)
2015-02-04 17:02               ` Vlastimil Babka [this message]
2015-02-04 19:24                 ` Michael Kerrisk (man-pages)
2015-02-05  1:07                   ` Minchan Kim
2015-02-06 15:41                     ` Michael Kerrisk (man-pages)
2015-02-09  6:46                       ` Minchan Kim
2015-02-09  9:13                         ` Michael Kerrisk (man-pages)
2015-02-05 15:41                   ` Michal Hocko
2015-02-06 15:57                     ` Michael Kerrisk (man-pages)
2015-02-06 20:45                       ` Michal Hocko
2015-02-09  6:50                       ` Minchan Kim
2015-02-04  0:09         ` Minchan Kim
2015-02-03 11:16     ` Mel Gorman
2015-02-03 15:21       ` Michal Hocko
2015-02-03 16:25         ` Michael Kerrisk (man-pages)
2015-02-03  9:47   ` Mel Gorman
2015-02-03 10:47     ` Kirill A. Shutemov
2015-02-03 11:21       ` Mel Gorman

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