linux-ext4 - Re: [PATCH 2/3] ext4: Context support

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Message-Id: <A65DE25A-54D6-4367-9CBD-E47A36B7E4AE@dilger.ca>
Date:	Thu, 14 Jun 2012 23:18:36 -0600
From:	Andreas Dilger <adilger@...ger.ca>
To:	Arnd Bergmann <arnd.bergmann@...aro.org>
Cc:	"Ted Ts'o" <tytso@....edu>,
	Alex Lemberg <Alex.Lemberg@...disk.com>,
	HYOJIN JEONG <syr.jeong@...sung.com>,
	Saugata Das <saugata.das@...aro.org>,
	Artem Bityutskiy <dedekind1@...il.com>,
	Saugata Das <saugata.das@...ricsson.com>,
	linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-mmc@...r.kernel.org, patches@...aro.org, venkat@...aro.org,
	"Luca Porzio (lporzio)" <lporzio@...ron.com>
Subject: Re: [PATCH 2/3] ext4: Context support

On 2012-06-14, at 3:55 PM, Arnd Bergmann wrote:
> My feeling is that we would actually benefit much more from the
> erase block alignment than from the context for the large files.
> 
> I think this is something we can do in the Linaro storage team.
> We actually have plans to also put the erase block size in the swap
> header, so we should be able to use the same code in mke2fs and mkswap,
> and potentially others. What we discussed in the storage team meeting
> today is that we start out by making ext4 aware of the erase block
> size through the superblock and aligning extents for large files to
> erase block boundaries.

Note that there are already the s_raid_stride and s_raid_stripe_width,
used by the ext4 allocator to align the start and size of allocations
on RAID systems.  The erase block size would be like s_raid_stride
(the minimum amount of data to allocate and write contiguously).

I don't know that there is a benefit to having a separate erase block
size, since in the end it means the same as s_raid_stride to the
allocator - make sure allocations/writes are aligned and sized on
multiples of this.

Cheers, Andreas





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