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Re: [PATCH v2] xfs: probe data buffer from page cache for unwritten exte

To: jeff.liu@xxxxxxxxxx
Subject: Re: [PATCH v2] xfs: probe data buffer from page cache for unwritten extents
From: Mark Tinguely <tinguely@xxxxxxx>
Date: Mon, 25 Jun 2012 11:13:05 -0500
Cc: xfs@xxxxxxxxxxx
In-reply-to: <4FE85C7B.3010909@xxxxxxxxxx>
References: <4FE85C7B.3010909@xxxxxxxxxx>
User-agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:9.0) Gecko/20120122 Thunderbird/9.0
On 06/25/12 07:41, Jeff Liu wrote:
Hello,

Using the start offset rather than map->br_startoff to calculate the starting 
page index could
get more accurate data offset in page cache probe routine.
With this refinement, the old max_t() could be able to remove too.

Thanks Mark for pointing this out!

-Jeff


Cc: Mark Tinguely<tinguely@xxxxxxx>
Signed-off-by: Jie Liu<jeff.liu@xxxxxxxxxx>

---

+                       /*
+                        * xfs_bmapi_read() can handle repeated hole regions,
+                        * hence it should not return two extents both are
+                        * holes.  If the 2nd extent is unwritten, there must
+                        * have data buffer resides in page cache.
+                        */
+                       BUG();


Looks great.

I hit the BUG() using a test with the following test:

 hole
 unwritten (treated as a hole)
 unwritten (treated as a hole)
 page of data.

I will send the current version of the test program.

--Mark.

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