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Re: [PATCH 1/2] xfs: introduce XFS_BMAPI_STACK_SWITCH

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH 1/2] xfs: introduce XFS_BMAPI_STACK_SWITCH
From: Mark Tinguely <tinguely@xxxxxxx>
Date: Fri, 05 Oct 2012 08:27:43 -0500
Cc: xfs@xxxxxxxxxxx
In-reply-to: <1349399219-13024-2-git-send-email-david@xxxxxxxxxxxxx>
References: <1349399219-13024-1-git-send-email-david@xxxxxxxxxxxxx> <1349399219-13024-2-git-send-email-david@xxxxxxxxxxxxx>
User-agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:9.0) Gecko/20120122 Thunderbird/9.0
On 10/04/12 20:06, Dave Chinner wrote:
From: Dave Chinner<dchinner@xxxxxxxxxx>

Certain allocation paths through xfs_bmapi_write() are in situations
where we have limited stack available. These are almost always in
the buffered IO writeback path when convertion delayed allocation
extents to real extents.

The current stack switch occurs for userdata allocations, which
means we also do stack switches for preallocation, direct IO and
unwritten extent conversion, even those these call chains have never
been implicated in a stack overrun.

Hence, let's target just the single stack overun offended for stack
switches. To do that, introduce a XFS_BMAPI_STACK_SWITCH flag that
the caller can pass xfs_bmapi_write() to indicate it should switch
stacks if it needs to do allocation.

Signed-off-by: Dave Chinner<dchinner@xxxxxxxxxx>

Looks good.

Reviewed-by: Mark Tinguely <tinguely@xxxxxxx>

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