linux-kernel - Re: __vmalloc() vs. GFP_NOIO/GFP

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Message-ID: <568A7663.80407@I-love.SAKURA.ne.jp>
Date:	Mon, 4 Jan 2016 22:40:51 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	Al Viro <viro@...IV.linux.org.uk>, linux-mm@...ck.org
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Dave Chinner <david@...morbit.com>,
	Ming Lei <ming.lei@...onical.com>
Subject: Re: __vmalloc() vs. GFP_NOIO/GFP_NOFS

On 2016/01/03 16:12, Al Viro wrote:
> Those, AFAICS, are such callers with GFP_NOIO; however, there's a shitload
> of GFP_NOFS ones.  XFS uses memalloc_noio_save(), but a _lot_ of other
> callers do not.  For example, all call chains leading to ceph_kvmalloc()
> pass GFP_NOFS and none of them is under memalloc_noio_save().  The same
> goes for GFS2 __vmalloc() callers, etc.  Again, quite a few of those probably
> do not need GFP_NOFS at all, but those that do would appear to have
> hard-to-trigger deadlocks.
> 
> Why do we do that in callers, though?  I.e. why not do something like this:

This problem is not specific to vmalloc(). It is difficult for
non-fs developers to determine whether they need to use GFP_NOFS than
GFP_KERNEL in their code. Can't we annotate GFP_NOFS/GFP_NOIO sections like
http://marc.info/?l=linux-mm&m=142797559822655 ?

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