From: Andrew Morton <akpm@osdl.org>
To: NeilBrown <neilb@suse.de>
Cc: linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org,
paul.clements@steeleye.com
Subject: Re: [PATCH 008 of 8] md/bitmap: Change md/bitmap file handling to use bmap to file blocks.
Date: Fri, 12 May 2006 10:47:50 -0700 [thread overview]
Message-ID: <20060512104750.0f5cb10a.akpm@osdl.org> (raw)
In-Reply-To: <1060512060809.8099@suse.de>
NeilBrown <neilb@suse.de> wrote:
>
> If md is asked to store a bitmap in a file, it tries to hold onto the
> page cache pages for that file, manipulate them directly, and call a
> cocktail of operations to write the file out. I don't believe this is
> a supportable approach.
erk. I think it's better than...
> This patch changes the approach to use the same approach as swap files.
> i.e. bmap is used to enumerate all the block address of parts of the file
> and we write directly to those blocks of the device.
That's going in at a much lower level. Even swapfiles don't assume
buffer_heads.
When playing with bmap() one needs to be careful that nobody has truncated
the file on you, else you end up writing to disk blocks which aren't part
of the file any more.
All this (and a set_fs(KERNEL_DS), ug) looks like a step backwards to me.
Operating at the pagecache a_ops level looked better, and more
filesystem-independent.
I haven't looked at this patch at all closely yet. Do I really need to?
next prev parent reply other threads:[~2006-05-12 17:45 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-05-12 6:07 [PATCH 000 of 8] md/bitmap: Introduction - rework management of bitmap files NeilBrown
2006-05-12 6:07 ` [PATCH 001 of 8] md/bitmap: Fix online removal of file-backed bitmaps NeilBrown
2006-05-12 6:07 ` [PATCH 002 of 8] md/bitmap: Remove bitmap writeback daemon NeilBrown
2006-05-12 17:40 ` Andrew Morton
2006-05-13 3:14 ` Neil Brown
2006-05-13 6:59 ` Andrew Morton
2006-05-12 6:07 ` [PATCH 003 of 8] md/bitmap: Cleaner separation of page attribute handlers in md/bitmap NeilBrown
2006-05-12 6:07 ` [PATCH 004 of 8] md/bitmap: Use set_bit etc for bitmap page attributes NeilBrown
2006-05-12 6:07 ` [PATCH 005 of 8] md/bitmap: Remove unnecessary page reference manipulations from md/bitmap code NeilBrown
2006-05-12 6:07 ` [PATCH 006 of 8] md/bitmap: Remove dead code from md/bitmap NeilBrown
2006-05-12 6:08 ` [PATCH 007 of 8] md/bitmap: Tidy up i_writecount handling in md/bitmap NeilBrown
2006-05-12 6:08 ` [PATCH 008 of 8] md/bitmap: Change md/bitmap file handling to use bmap to file blocks NeilBrown
2006-05-12 17:47 ` Andrew Morton [this message]
2006-05-13 3:46 ` Neil Brown
2006-05-13 6:59 ` Andrew Morton
2006-05-13 15:29 ` Paul Clements
2006-05-13 15:42 ` Andrew Morton
2006-05-14 11:15 ` Neil Brown
2006-05-14 11:22 ` Andrew Morton
2006-05-15 0:26 ` Neil Brown
2006-05-15 21:04 ` Andrew Morton
2006-05-15 23:03 ` Neil Brown
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