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From: Konstantin Khlebnikov <email@example.com>
To: Hugh Dickins <firstname.lastname@example.org>
Cc: Andrew Morton <email@example.com>,
Jerome Marchand <firstname.lastname@example.org>,
"Wang, Yalin" <Yalin.Wang@sonymobile.com>,
"Kirill A. Shutemov" <email@example.com>,
Subject: Re: [RFC] mm:change meminfo cached calculation
Date: Sun, 11 Jan 2015 12:23:56 +0400 [thread overview]
Message-ID: <CALYGNiM11DRqJ5OT+27Db3O_0w7v7iMHquRH+V-gi=rjYy4hKA@mail.gmail.com> (raw)
On Wed, Jan 7, 2015 at 5:03 AM, Hugh Dickins <firstname.lastname@example.org> wrote:
> On Tue, 6 Jan 2015, Andrew Morton wrote:
>> On Tue, 6 Jan 2015 17:04:33 -0800 (PST) Hugh Dickins <email@example.com> wrote:
>> > On Tue, 6 Jan 2015, Andrew Morton wrote:
>> > > On Fri, 26 Dec 2014 19:56:49 +0800 "Wang, Yalin" <Yalin.Wang@sonymobile.com> wrote:
>> > >
>> > > > This patch subtract sharedram from cached,
>> > > > sharedram can only be swap into swap partitions,
>> > > > they should be treated as swap pages, not as cached pages.
>> > > >
>> > > > ...
>> > > >
>> > > > --- a/fs/proc/meminfo.c
>> > > > +++ b/fs/proc/meminfo.c
>> > > > @@ -45,7 +45,7 @@ static int meminfo_proc_show(struct seq_file *m, void *v)
>> > > > committed = percpu_counter_read_positive(&vm_committed_as);
>> > > >
>> > > > cached = global_page_state(NR_FILE_PAGES) -
>> > > > - total_swapcache_pages() - i.bufferram;
>> > > > + total_swapcache_pages() - i.bufferram - i.sharedram;
>> > > > if (cached < 0)
>> > > > cached = 0;
>> > >
>> > > Documentation/filesystems/proc.txt says
>> > >
>> > > : Cached: in-memory cache for files read from the disk (the
>> > > : pagecache). Doesn't include SwapCached
>> > >
>> > > So yes, I guess it should not include shmem.
>> > >
>> > > And why not do this as well?
>> > >
>> > >
>> > > --- a/Documentation/filesystems/proc.txt~mm-change-meminfo-cached-calculation-fix
>> > > +++ a/Documentation/filesystems/proc.txt
>> > > @@ -811,7 +811,7 @@ MemAvailable: An estimate of how much me
>> > > Buffers: Relatively temporary storage for raw disk blocks
>> > > shouldn't get tremendously large (20MB or so)
>> > > Cached: in-memory cache for files read from the disk (the
>> > > - pagecache). Doesn't include SwapCached
>> > > + pagecache). Doesn't include SwapCached or Shmem.
>> > > SwapCached: Memory that once was swapped out, is swapped back in but
>> > > still also is in the swapfile (if memory is needed it
>> > > doesn't need to be swapped out AGAIN because it is already
>> > Whoa. Changes of this kind would have made good sense about 14 years ago.
>> > And there's plenty more which would benefit from having anon/shmem/file
>> > properly distinguished. But how can we make such a change now,
>> > breaking everything that has made its own sense of these counts?
>> That's what I was wondering, but I was having some trouble picking a
>> situation where it mattered much.
> If it doesn't matter, then we don't need to change it.
>> What's the problematic scenario
>> here? Userspace that is taking Cached, saying "that was silly" and
>> subtracting Shmem from it by hand?
> Someone a long time ago saw "that was silly", worked out it was because
> of Shmem, adjusted their scripts or whatever accordingly, and has run
> happily ever since.
Totally agree. I know some of these guys.
But that's here not for so long time, 'Shmem' has appeared only in 2.6.32.
>> I suppose that as nobody knows we should err on the side of caution and
>> leave this alone. But the situation is pretty sad - it would be nice
>> to make the code agree with the documentation at least.
> By all means fix the documentation. And work on a /proc/meminfo.2015
> which has sensibly differentiated counts (and probably omits that
> wonderful Linux 2.2-compatible "Buffers").
'Buffers' is actually very useful. Ext4 keeps almost all metadata in
Meminfo has a bigger and much more confusing problem: there is no subset of
fields which sums to all ram. Some paged allocations are showed nowhere.
Probably it would be good to show that 'Untracked' memory as well,
Total - Free - Cached - Buffers - Slab - PageTables - KernelStack - AnonPages.
(fix me if I'm wrong =)
> But there's more to do than I can think of. Cc'ing Jerome who has a
> particular interest in this (no, I haven't forgotten his patches,
> but nor have I had a moment to reconsider them).
next prev parent reply other threads:[~2015-01-11 8:24 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-12-05 8:57 [RFC] mm:add KPF_ZERO_PAGE flag for /proc/kpageflags Wang, Yalin
2014-12-05 9:20 ` Konstantin Khlebnikov
2014-12-05 10:22 ` Wang, Yalin
2014-12-05 22:31 ` Andrew Morton
2014-12-08 2:00 ` [RFC V4] " Wang, Yalin
2014-12-08 11:46 ` Kirill A. Shutemov
2014-12-09 3:24 ` [RFC V5] " Wang, Yalin
2014-12-10 7:22 ` [RFC] mm:fix zero_page huge_zero_page rss/pss statistic Wang, Yalin
2014-12-10 11:05 ` Kirill A. Shutemov
2014-12-12 1:59 ` Wang, Yalin
2014-12-12 11:10 ` Kirill A. Shutemov
2014-12-10 17:06 ` [RFC V5] mm:add KPF_ZERO_PAGE flag for /proc/kpageflags Konstantin Khlebnikov
2014-12-12 3:30 ` [RFC] discard task stack pages instead of pageout into swap partition Wang, Yalin
2014-12-18 3:50 ` [RFC] MADV_FREE doesn't work when doesn't have " Wang, Yalin
2014-12-19 1:04 ` Minchan Kim
2014-12-19 6:54 ` Wang, Yalin
2014-12-22 10:30 ` Konstantin Khlebnikov
2014-12-26 11:56 ` [RFC] mm:change meminfo cached calculation Wang, Yalin
2015-01-07 0:43 ` Andrew Morton
2015-01-07 1:04 ` Hugh Dickins
2015-01-07 1:25 ` Andrew Morton
2015-01-07 2:03 ` Hugh Dickins
2015-01-11 8:23 ` Konstantin Khlebnikov [this message]
2014-12-05 10:21 ` [RFC V2] mm:add KPF_ZERO_PAGE flag for /proc/kpageflags Wang, Yalin
2014-12-05 11:05 ` Kirill A. Shutemov
2014-12-08 1:51 ` [RFC V3] " Wang, Yalin
2014-12-08 7:47 ` [PATCH] mm:add VM_BUG_ON() for page_mapcount() Wang, Yalin
2014-12-08 11:50 ` Kirill A. Shutemov
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