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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <49986EEA.1020405@redhat.com>
Date:	Sun, 15 Feb 2009 13:37:14 -0600
From:	Eric Sandeen <sandeen@...hat.com>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
CC:	Theodore Tso <tytso@....edu>, linux-ext4@...r.kernel.org
Subject: Re: ext4 not currently doing (much) multi-block allocation?

Aneesh Kumar K.V wrote:
> On Sun, Feb 15, 2009 at 08:36:18AM -0500, Theodore Tso wrote:
>> 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).
> 
> 
> That bh>b_size indicate multiple blocks. 

I never did like this overloading of a buffer head for this sort of
purpose, for this (sometimes confusing) reason, but it's done throughout
the kernel... :)

But, maybe a comment would be in order just to make it clear  "This is a
mapping BH" or something.

-Eric

> we do the below in mpage_add_bh_to_extent
> 
> 2024         if (logical == next && (bh->b_state & BH_FLAGS) == lbh->b_state) {
> 2025                 lbh->b_size += b_size;
> 2026                 return;
> 2027         }
> 
>> Put another way, where is the call to ext4_get_blocks_wrap() which
>> does the multi-block request?  I don't see it...
>>
> 

--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html