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From: Hugh Dickins <email@example.com>
To: Andrew Morton <firstname.lastname@example.org>
Cc: Jerome Marchand <email@example.com>,
Hugh Dickins <firstname.lastname@example.org>,
"Wang, Yalin" <Yalin.Wang@sonymobile.com>,
Konstantin Khlebnikov <email@example.com>,
"Kirill A. Shutemov" <firstname.lastname@example.org>,
Subject: Re: [RFC] mm:change meminfo cached calculation
Date: Tue, 6 Jan 2015 18:03:47 -0800 (PST) [thread overview]
Message-ID: <alpine.LSU.email@example.com> (raw)
On Tue, 6 Jan 2015, Andrew Morton wrote:
> On Tue, 6 Jan 2015 17:04:33 -0800 (PST) Hugh Dickins <firstname.lastname@example.org> 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.
> 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").
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:[~2015-01-07 2:03 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 [this message]
2015-01-11 8:23 ` Konstantin Khlebnikov
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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