linux-ext4 - Re: [PATCH 1/2] fs: Do not dispatch FITRIM through separate super

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Date:	Fri, 19 Nov 2010 10:24:52 -0500
From:	Mark Lord <kernel@...savvy.com>
To:	Christoph Hellwig <hch@...radead.org>
CC:	Greg Freemyer <greg.freemyer@...il.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	James Bottomley <James.Bottomley@...e.de>,
	Jeff Moyer <jmoyer@...hat.com>,
	Matthew Wilcox <matthew@....cx>,
	Josef Bacik <josef@...hat.com>,
	Lukas Czerner <lczerner@...hat.com>, tytso@....edu,
	linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, sandeen@...hat.com
Subject: Re: [PATCH 1/2] fs: Do not dispatch FITRIM through separate super_operation

On 10-11-19 09:54 AM, Christoph Hellwig wrote:
> On Fri, Nov 19, 2010 at 09:48:12AM -0500, Mark Lord wrote:
>> I'm not sure about the issues on "adapting the block layer" ?
>> For FITRIM, the blocks being trimmed would be reserved at the fs level,
>> before issuing the discard for them.  So ordering through the block layer
>> shouldn't matter much for it.  Does that simplify things?
>>
>> I see FITRIM just allocating a page to hold the ranges (for the>1 case)
>> and passing that page down through the layers to libata (or any other
>> LLD that supports>1 ranges).
>
> Ordering should not be an issue.  What were problems when I tried this
> before is that we currently assume in the block layer that discard
> bios have a valid bi_sector/bi_size, which is already needed e.g. for
> the trivial remapping use for partitions and that they don't have
> a payload.  You'd need to teach various places that discard payloads
> may have a payload, which contains multiple ranges that have a
> sector/len tuple that needs to be remapped and checked in various
> places.

I wonder if this can be treated more like how SG_IO does things?
The SG_IO mechanism seems to have no issues passing through stuff
like this, so perhaps we could implement something in a similar fashion?

-ml
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