linux-ext4 - Re: [PATCH 6/6] mbcache2: Use referenced bit instead of LRU

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Date:	Mon, 14 Dec 2015 11:34:00 +0100
From:	Jan Kara <jack@...e.cz>
To:	Andreas Grünbacher 
	<andreas.gruenbacher@...il.com>
Cc:	Jan Kara <jack@...e.cz>, Ted Tso <tytso@....edu>,
	linux-ext4@...r.kernel.org, Laurent GUERBY <laurent@...rby.net>,
	Andreas Dilger <adilger@...ger.ca>
Subject: Re: [PATCH 6/6] mbcache2: Use referenced bit instead of LRU

On Sat 12-12-15 00:58:51, Andreas Grünbacher wrote:
> Jan,
> 
> 2015-12-09 18:57 GMT+01:00 Jan Kara <jack@...e.cz>:
> > Currently we maintain perfect LRU list by moving entry to the tail of
> > the list when it gets used. However these operations on cache-global
> > list are relatively expensive.
> >
> > In this patch we switch to lazy updates of LRU list. Whenever entry gets
> > used, we set a referenced bit in it. When reclaiming entries, we give
> > referenced entries another round in the LRU.
> >
> > In my testing this logic gives about 30% boost to workloads with mostly
> > unique xattr blocks (e.g. xattr-bench with 10 files and 10000 unique
> > xattr values).
> 
> I find it quite confusing that with this patch applied, structs
> mb2_cache and mb2_cache_entry still contain fields with "lru" in their
> name.

Yes, it's somewhat confusing so if you have a better suggestion for the
name I can change it. Maybe cache_list to suggest it's a list of all
entries in the cache?

BTW, I have kept the name to mirror what we do with inodes which use the
same naming and LRU scheme. But probably there's no strong reason to adhere
to the naming scheme.

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