linux-ext4 - Re: [PATCH 0/2] new APIs to allocate buffer-cache for superblock in non-movable area

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Message-ID: <20140818121146.GD9603@quack.suse.cz>
Date:	Mon, 18 Aug 2014 14:11:46 +0200
From:	Jan Kara <jack@...e.cz>
To:	Gioh Kim <gioh.kim@....com>
Cc:	Theodore Ts'o <tytso@....edu>, Jan Kara <jack@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	linux-ext4@...r.kernel.org, Minchan Kim <minchan@...nel.org>,
	Joonsoo Kim <js1304@...il.com>,
	이건호 <gunho.lee@....com>
Subject: Re: [PATCH 0/2] new APIs to allocate buffer-cache for superblock in
 non-movable area

On Mon 18-08-14 13:44:38, Gioh Kim wrote:
> 
> 
> 2014-08-18 오후 12:24, Theodore Ts'o 쓴 글:
> >On Mon, Aug 18, 2014 at 10:15:32AM +0900, Gioh Kim wrote:
> >>
> >>My test platform has totally 1GB memory, 256MB for CMA and 768MB for normal.
> >>I applied Joonsoo's patch: https://lkml.org/lkml/2014/5/28/64, so that
> >>3/4 of allocation take place in normal area and 1/4 allocation take place in CMA area.
> >>
> >>And my platform has 4 ext4 partitions. Each ext4 partition has 2 page caches for superblock that
> >>are what this patch tries to move to out of CMA area.
> >>Therefore there are 8 page caches (8 pages size) that can prevent page migration.
> >
> >Yes, but are you actually *using* the ext4 partitions for anything?
> >If this is a realistic real world use case, file systems are used to
> >store, well, files, and that means there will be inodes and dentry
> >cache entries that will also be allocated.  Does your test scenario
> >reflect real world usage?
> 
> Yes. I'm working for LG Electronics.
> My test platform is currently selling item in the market.
> And also I test my patch when my platform is working as if real user uses it.
  Great, this is exactly what I was looking for. So if it really makes
your usecase work I don't have objections to your solution (after you
change what Andrew suggested).

> I think the page caches of the inodes and dentry are held for short time.
> I can see pairs of get_bh and put_bh in inodes/dentry handling.
> 
> I think inodes is allocated by kmem_cache_alloc in ext4_alloc_inode().
> It is non-movable area allocation.
  I guess the hold time depends on what storage do you use in your product
(flash?) and how loaded it is.

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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