linux-kernel - Re: [PATCH v7 9/9] block: Avoid deadlocks with bio allocation by stacking drivers

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Message-ID: <20120903011752.GC20060@moria.home.lan>
Date:	Sun, 2 Sep 2012 18:17:52 -0700
From:	Kent Overstreet <koverstreet@...gle.com>
To:	Dave Chinner <david@...morbit.com>
Cc:	Vivek Goyal <vgoyal@...hat.com>,
	Mikulas Patocka <mpatocka@...hat.com>,
	linux-bcache@...r.kernel.org, linux-kernel@...r.kernel.org,
	dm-devel@...hat.com, tj@...nel.org, bharrosh@...asas.com,
	Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH v7 9/9] block: Avoid deadlocks with bio allocation by
 stacking drivers

On Mon, Sep 03, 2012 at 10:49:27AM +1000, Dave Chinner wrote:
> Given that we are working around stack depth issues in the
> filesystems already in several places, and now it seems like there's
> a reason to work around it in the block layers as well, shouldn't we
> simply increase the default stack size rather than introduce
> complexity and performance regressions to try and work around not
> having enough stack?
> 
> I mean, we can deal with it like the ia32 4k stack issue was dealt
> with (i.e. ignore those stupid XFS people, that's an XFS bug), or
> we can face the reality that storage stacks have become so complex
> that 8k is no longer a big enough stack for a modern system....

I'm not arguing against increasing the default stack size (I really
don't have an opinion there) - but it's not a solution for the block
layer, as stacking block devices can require an unbounded amount of
stack without the generic_make_request() convert recursion-to-iteration
thing.
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