From: Minchan Kim <minchan@kernel.org>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>,
Dave Hansen <dave.hansen@intel.com>, Mel Gorman <mgorman@suse.de>,
linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
mtk.manpages@gmail.com, linux-man@vger.kernel.org,
Rik van Riel <riel@redhat.com>
Subject: Re: MADV_DONTNEED semantics? Was: [RFC PATCH] mm: madvise: Ignore repeated MADV_DONTNEED hints
Date: Wed, 4 Feb 2015 09:09:21 +0900 [thread overview]
Message-ID: <20150204000921.GC3583@blaptop> (raw)
In-Reply-To: <54D0B43D.8000209@suse.cz>
On Tue, Feb 03, 2015 at 12:42:53PM +0100, Vlastimil Babka wrote:
> On 02/03/2015 11:53 AM, Kirill A. Shutemov wrote:
> > On Tue, Feb 03, 2015 at 09:19:15AM +0100, Vlastimil Babka wrote:
> >> [CC linux-api, man pages]
> >>
> >> On 02/02/2015 11:22 PM, Dave Hansen wrote:
> >> > On 02/02/2015 08:55 AM, Mel Gorman wrote:
> >> >> This patch identifies when a thread is frequently calling MADV_DONTNEED
> >> >> on the same region of memory and starts ignoring the hint. On an 8-core
> >> >> single-socket machine this was the impact on ebizzy using glibc 2.19.
> >> >
> >> > The manpage, at least, claims that we zero-fill after MADV_DONTNEED is
> >> > called:
> >> >
> >> >> MADV_DONTNEED
> >> >> Do not expect access in the near future. (For the time being, the application is finished with the given range, so the kernel can free resources
> >> >> associated with it.) Subsequent accesses of pages in this range will succeed, but will result either in reloading of the memory contents from the
> >> >> underlying mapped file (see mmap(2)) or zero-fill-on-demand pages for mappings without an underlying file.
> >> >
> >> > So if we have anything depending on the behavior that it's _always_
> >> > zero-filled after an MADV_DONTNEED, this will break it.
> >>
> >> OK, so that's a third person (including me) who understood it as a zero-fill
> >> guarantee. I think the man page should be clarified (if it's indeed not
> >> guaranteed), or we have a bug.
> >>
> >> The implementation actually skips MADV_DONTNEED for
> >> VM_LOCKED|VM_HUGETLB|VM_PFNMAP vma's.
> >
> > It doesn't skip. It fails with -EINVAL. Or I miss something.
>
> No, I missed that. Thanks for pointing out. The manpage also explains EINVAL in
> this case:
>
> * The application is attempting to release locked or shared pages (with
> MADV_DONTNEED).
>
> - 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.
>
> >> - 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.
>
> I still wouldnt be sure just by reading the man page that the clearing is
> guaranteed whenever I dont get an error return value, though,
>
IMHO,
Man page said
"MADV_DONTNEED: Subsequent accesses of pages in this range will succeed,
but will result either in reloading of the memory contents from the
underlying mapped file (see mmap(2)) or zero-fill-on-demand pages
for mappings without an underlying file."
Heap by allocated by malloc(3) is anonymous page so it's a mapping
withtout an underlying file so userspace can expect zero-fill.
Man page said
"EINVAL: The application is attempting to release locked or
shared pages (with MADV_DONTNEED)"
So, user can expect the call on area by allocated by malloc(3)
if he doesn't call mlock will always be successful.
Man page said
"madivse: This call does not influence the semantics of the application
(except in the case of MADV_DONTNEED)"
So, we shouldn't break MADV_DONTNEED's semantic which free pages
instantly. It's a long time semantic and it was one of arguable issues
on MADV_FREE Rik had tried long time ago to replace MADV_DONTNEED
with MADV_FREE.
--
Kind regards,
Minchan Kim
WARNING: multiple messages have this Message-ID (diff)
From: Minchan Kim <minchan-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
To: Vlastimil Babka <vbabka-AlSwsSmVLrQ@public.gmane.org>
Cc: "Kirill A. Shutemov"
<kirill-oKw7cIdHH8eLwutG50LtGA@public.gmane.org>,
Dave Hansen <dave.hansen-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>,
Mel Gorman <mgorman-l3A5Bk7waGM@public.gmane.org>,
linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org,
Andrew Morton
<akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>,
linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org,
linux-man-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
Rik van Riel <riel-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Subject: Re: MADV_DONTNEED semantics? Was: [RFC PATCH] mm: madvise: Ignore repeated MADV_DONTNEED hints
Date: Wed, 4 Feb 2015 09:09:21 +0900 [thread overview]
Message-ID: <20150204000921.GC3583@blaptop> (raw)
In-Reply-To: <54D0B43D.8000209-AlSwsSmVLrQ@public.gmane.org>
On Tue, Feb 03, 2015 at 12:42:53PM +0100, Vlastimil Babka wrote:
> On 02/03/2015 11:53 AM, Kirill A. Shutemov wrote:
> > On Tue, Feb 03, 2015 at 09:19:15AM +0100, Vlastimil Babka wrote:
> >> [CC linux-api, man pages]
> >>
> >> On 02/02/2015 11:22 PM, Dave Hansen wrote:
> >> > On 02/02/2015 08:55 AM, Mel Gorman wrote:
> >> >> This patch identifies when a thread is frequently calling MADV_DONTNEED
> >> >> on the same region of memory and starts ignoring the hint. On an 8-core
> >> >> single-socket machine this was the impact on ebizzy using glibc 2.19.
> >> >
> >> > The manpage, at least, claims that we zero-fill after MADV_DONTNEED is
> >> > called:
> >> >
> >> >> MADV_DONTNEED
> >> >> Do not expect access in the near future. (For the time being, the application is finished with the given range, so the kernel can free resources
> >> >> associated with it.) Subsequent accesses of pages in this range will succeed, but will result either in reloading of the memory contents from the
> >> >> underlying mapped file (see mmap(2)) or zero-fill-on-demand pages for mappings without an underlying file.
> >> >
> >> > So if we have anything depending on the behavior that it's _always_
> >> > zero-filled after an MADV_DONTNEED, this will break it.
> >>
> >> OK, so that's a third person (including me) who understood it as a zero-fill
> >> guarantee. I think the man page should be clarified (if it's indeed not
> >> guaranteed), or we have a bug.
> >>
> >> The implementation actually skips MADV_DONTNEED for
> >> VM_LOCKED|VM_HUGETLB|VM_PFNMAP vma's.
> >
> > It doesn't skip. It fails with -EINVAL. Or I miss something.
>
> No, I missed that. Thanks for pointing out. The manpage also explains EINVAL in
> this case:
>
> * The application is attempting to release locked or shared pages (with
> MADV_DONTNEED).
>
> - 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.
>
> >> - 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.
>
> I still wouldnt be sure just by reading the man page that the clearing is
> guaranteed whenever I dont get an error return value, though,
>
IMHO,
Man page said
"MADV_DONTNEED: Subsequent accesses of pages in this range will succeed,
but will result either in reloading of the memory contents from the
underlying mapped file (see mmap(2)) or zero-fill-on-demand pages
for mappings without an underlying file."
Heap by allocated by malloc(3) is anonymous page so it's a mapping
withtout an underlying file so userspace can expect zero-fill.
Man page said
"EINVAL: The application is attempting to release locked or
shared pages (with MADV_DONTNEED)"
So, user can expect the call on area by allocated by malloc(3)
if he doesn't call mlock will always be successful.
Man page said
"madivse: This call does not influence the semantics of the application
(except in the case of MADV_DONTNEED)"
So, we shouldn't break MADV_DONTNEED's semantic which free pages
instantly. It's a long time semantic and it was one of arguable issues
on MADV_FREE Rik had tried long time ago to replace MADV_DONTNEED
with MADV_FREE.
--
Kind regards,
Minchan Kim
WARNING: multiple messages have this Message-ID (diff)
From: Minchan Kim <minchan@kernel.org>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>,
Dave Hansen <dave.hansen@intel.com>, Mel Gorman <mgorman@suse.de>,
linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
mtk.manpages@gmail.com, linux-man@vger.kernel.org,
Rik van Riel <riel@redhat.com>
Subject: Re: MADV_DONTNEED semantics? Was: [RFC PATCH] mm: madvise: Ignore repeated MADV_DONTNEED hints
Date: Wed, 4 Feb 2015 09:09:21 +0900 [thread overview]
Message-ID: <20150204000921.GC3583@blaptop> (raw)
In-Reply-To: <54D0B43D.8000209@suse.cz>
On Tue, Feb 03, 2015 at 12:42:53PM +0100, Vlastimil Babka wrote:
> On 02/03/2015 11:53 AM, Kirill A. Shutemov wrote:
> > On Tue, Feb 03, 2015 at 09:19:15AM +0100, Vlastimil Babka wrote:
> >> [CC linux-api, man pages]
> >>
> >> On 02/02/2015 11:22 PM, Dave Hansen wrote:
> >> > On 02/02/2015 08:55 AM, Mel Gorman wrote:
> >> >> This patch identifies when a thread is frequently calling MADV_DONTNEED
> >> >> on the same region of memory and starts ignoring the hint. On an 8-core
> >> >> single-socket machine this was the impact on ebizzy using glibc 2.19.
> >> >
> >> > The manpage, at least, claims that we zero-fill after MADV_DONTNEED is
> >> > called:
> >> >
> >> >> MADV_DONTNEED
> >> >> Do not expect access in the near future. (For the time being, the application is finished with the given range, so the kernel can free resources
> >> >> associated with it.) Subsequent accesses of pages in this range will succeed, but will result either in reloading of the memory contents from the
> >> >> underlying mapped file (see mmap(2)) or zero-fill-on-demand pages for mappings without an underlying file.
> >> >
> >> > So if we have anything depending on the behavior that it's _always_
> >> > zero-filled after an MADV_DONTNEED, this will break it.
> >>
> >> OK, so that's a third person (including me) who understood it as a zero-fill
> >> guarantee. I think the man page should be clarified (if it's indeed not
> >> guaranteed), or we have a bug.
> >>
> >> The implementation actually skips MADV_DONTNEED for
> >> VM_LOCKED|VM_HUGETLB|VM_PFNMAP vma's.
> >
> > It doesn't skip. It fails with -EINVAL. Or I miss something.
>
> No, I missed that. Thanks for pointing out. The manpage also explains EINVAL in
> this case:
>
> * The application is attempting to release locked or shared pages (with
> MADV_DONTNEED).
>
> - 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.
>
> >> - 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.
>
> I still wouldnt be sure just by reading the man page that the clearing is
> guaranteed whenever I dont get an error return value, though,
>
IMHO,
Man page said
"MADV_DONTNEED: Subsequent accesses of pages in this range will succeed,
but will result either in reloading of the memory contents from the
underlying mapped file (see mmap(2)) or zero-fill-on-demand pages
for mappings without an underlying file."
Heap by allocated by malloc(3) is anonymous page so it's a mapping
withtout an underlying file so userspace can expect zero-fill.
Man page said
"EINVAL: The application is attempting to release locked or
shared pages (with MADV_DONTNEED)"
So, user can expect the call on area by allocated by malloc(3)
if he doesn't call mlock will always be successful.
Man page said
"madivse: This call does not influence the semantics of the application
(except in the case of MADV_DONTNEED)"
So, we shouldn't break MADV_DONTNEED's semantic which free pages
instantly. It's a long time semantic and it was one of arguable issues
on MADV_FREE Rik had tried long time ago to replace MADV_DONTNEED
with MADV_FREE.
--
Kind regards,
Minchan Kim
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2015-02-04 0:09 UTC|newest]
Thread overview: 76+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-02-02 16:55 [RFC PATCH] mm: madvise: Ignore repeated MADV_DONTNEED hints Mel Gorman
2015-02-02 16:55 ` Mel Gorman
2015-02-02 22:05 ` Andrew Morton
2015-02-02 22:05 ` Andrew Morton
2015-02-02 22:18 ` Mel Gorman
2015-02-02 22:18 ` Mel Gorman
2015-02-02 22:35 ` Andrew Morton
2015-02-02 22:35 ` Andrew Morton
2015-02-03 0:26 ` Davidlohr Bueso
2015-02-03 0:26 ` Davidlohr Bueso
2015-02-03 10:50 ` Mel Gorman
2015-02-03 10:50 ` Mel Gorman
2015-02-05 21:44 ` Rik van Riel
2015-02-05 21:44 ` Rik van Riel
2015-02-02 22:22 ` Dave Hansen
2015-02-02 22:22 ` Dave Hansen
2015-02-03 8:19 ` MADV_DONTNEED semantics? Was: " Vlastimil Babka
2015-02-03 8:19 ` Vlastimil Babka
2015-02-03 10:53 ` Kirill A. Shutemov
2015-02-03 10:53 ` Kirill A. Shutemov
2015-02-03 10:53 ` Kirill A. Shutemov
2015-02-03 11:42 ` Vlastimil Babka
2015-02-03 11:42 ` Vlastimil Babka
2015-02-03 16:20 ` Michael Kerrisk (man-pages)
2015-02-03 16:20 ` Michael Kerrisk (man-pages)
2015-02-04 13:46 ` Vlastimil Babka
2015-02-04 13:46 ` Vlastimil Babka
2015-02-04 13:46 ` Vlastimil Babka
2015-02-04 14:00 ` Michael Kerrisk (man-pages)
2015-02-04 14:00 ` Michael Kerrisk (man-pages)
2015-02-04 14:00 ` Michael Kerrisk (man-pages)
2015-02-04 17:02 ` Vlastimil Babka
2015-02-04 17:02 ` Vlastimil Babka
2015-02-04 19:24 ` Michael Kerrisk (man-pages)
2015-02-04 19:24 ` Michael Kerrisk (man-pages)
2015-02-04 19:24 ` Michael Kerrisk (man-pages)
2015-02-05 1:07 ` Minchan Kim
2015-02-05 1:07 ` Minchan Kim
2015-02-05 1:07 ` Minchan Kim
2015-02-06 15:41 ` Michael Kerrisk (man-pages)
2015-02-06 15:41 ` Michael Kerrisk (man-pages)
2015-02-06 15:41 ` Michael Kerrisk (man-pages)
2015-02-09 6:46 ` Minchan Kim
2015-02-09 6:46 ` Minchan Kim
2015-02-09 6:46 ` Minchan Kim
2015-02-09 9:13 ` Michael Kerrisk (man-pages)
2015-02-09 9:13 ` Michael Kerrisk (man-pages)
2015-02-05 15:41 ` Michal Hocko
2015-02-05 15:41 ` Michal Hocko
2015-02-05 15:41 ` Michal Hocko
2015-02-06 15:57 ` Michael Kerrisk (man-pages)
2015-02-06 15:57 ` Michael Kerrisk (man-pages)
2015-02-06 15:57 ` Michael Kerrisk (man-pages)
2015-02-06 20:45 ` Michal Hocko
2015-02-06 20:45 ` Michal Hocko
2015-02-06 20:45 ` Michal Hocko
2015-02-09 6:50 ` Minchan Kim
2015-02-09 6:50 ` Minchan Kim
2015-02-09 6:50 ` Minchan Kim
2015-02-04 0:09 ` Minchan Kim [this message]
2015-02-04 0:09 ` Minchan Kim
2015-02-04 0:09 ` Minchan Kim
2015-02-03 11:16 ` Mel Gorman
2015-02-03 11:16 ` Mel Gorman
2015-02-03 15:21 ` Michal Hocko
2015-02-03 15:21 ` Michal Hocko
2015-02-03 15:21 ` Michal Hocko
2015-02-03 16:25 ` Michael Kerrisk (man-pages)
2015-02-03 16:25 ` Michael Kerrisk (man-pages)
2015-02-03 16:25 ` Michael Kerrisk (man-pages)
2015-02-03 9:47 ` Mel Gorman
2015-02-03 9:47 ` Mel Gorman
2015-02-03 10:47 ` Kirill A. Shutemov
2015-02-03 10:47 ` Kirill A. Shutemov
2015-02-03 11:21 ` Mel Gorman
2015-02-03 11:21 ` Mel Gorman
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