linux-ext4 - Re: ext4 not currently doing (much) multi-block allocation?

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Message-ID: <20090215133618.GE10706@mini-me.lan>
Date:	Sun, 15 Feb 2009 08:36:18 -0500
From:	Theodore Tso <tytso@....edu>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: ext4 not currently doing (much) multi-block allocation?

On Sun, Feb 15, 2009 at 04:35:28PM +0530, Aneesh Kumar K.V wrote:
> Here is how it works. During writepages we loop through the dirty pages
> and build largest contiguous block extent (mpage_add_bh_to_extent). Then we call
> mpage_da_map_blocks. mpage_da_map_blocks does the mutli block request.
> Once we have the blocks allocated we map these blocks to the pages. And
> then we writeback one page at a time using writepage callback.

mpage_da_map_blocks() calls mpd->get_block, which is set to
ext4_da_get_block_write(), which allocates a single block at a time
(max_blocks is set to bh->b_size >> inode->i_blkbits).

Put another way, where is the call to ext4_get_blocks_wrap() which
does the multi-block request?  I don't see it...

						- Ted
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