From: Dan Magenheimer <dan.magenheimer@oracle.com>
To: Dan Magenheimer <dan.magenheimer@oracle.com>,
Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>,
Luigi Semenzato <semenzato@google.com>,
linux-mm@kvack.org, Bob Liu <lliubbo@gmail.com>
Subject: RE: zram /proc/swaps accounting weirdness
Date: Tue, 11 Dec 2012 17:12:18 -0800 (PST) [thread overview]
Message-ID: <9c96c9e7-4f6e-4e78-a207-009293c37b89@default> (raw)
In-Reply-To: <d4ab3d29-f29d-4236-bbba-d93b633a18e7@default>
> From: Dan Magenheimer
> Subject: RE: zram /proc/swaps accounting weirdness
>
> > > Can you explain how this could happen if num_writes never
> > > exceeded 1863? This may be harmless in the case where
> >
> > Odd.
> > I tried to reproduce it with zram and real swap device without
> > zcache but failed. Does the problem happen only if enabling zcache
> > together?
>
> I also cannot reproduce it with only zram, without zcache.
> I can only reproduce with zcache+zram. Since zcache will
> only "fall through" to zram when the frontswap_store() call
> in swap_writepage() fails, I wonder if in both cases swap_writepage()
> is being called in large (e.g. SWAPFILE_CLUSTER-sized) blocks
> of pages? When zram-only, the entire block of pages always gets
> sent to zram, but with zcache only a small randomly-positioned
> fraction fail frontswap_store(), but the SWAPFILE_CLUSTER-sized
> blocks have already been pre-reserved on the swap device and
> become only partially-filled?
Urk. Never mind. My bad. When a swap page is compressed in
zcache, it gets accounted in the swap subsystem as an "inuse"
page for the backing swap device. (Frontswap provides a
page-by-page "fronting store" for the swap device.) That explains
why Used is so high for the "zram swap device" even though
zram has only compressed a fraction of the pages... the
remaining (much larger) number of pages have been compressed
by/in zcache.
Move along, there are no droids here. :-(
Dan
--
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:[~2012-12-12 1:12 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-12-07 23:57 zram /proc/swaps accounting weirdness Dan Magenheimer
2012-12-10 3:15 ` Bob Liu
2012-12-12 0:22 ` Dan Magenheimer
2012-12-11 6:26 ` Minchan Kim
2012-12-12 0:34 ` Dan Magenheimer
2012-12-12 1:12 ` Dan Magenheimer [this message]
2013-02-17 1:52 ` Simon Jeons
2013-02-18 17:54 ` Dan Magenheimer
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=9c96c9e7-4f6e-4e78-a207-009293c37b89@default \
--to=dan.magenheimer@oracle.com \
--cc=linux-mm@kvack.org \
--cc=lliubbo@gmail.com \
--cc=minchan@kernel.org \
--cc=ngupta@vflare.org \
--cc=semenzato@google.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).