linux-ext4 - Re: ext2_block_alloc

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Message-ID: <170fa0d20812221856j4c660384nc2ac693ca8fd0ba4@mail.gmail.com>
Date:	Mon, 22 Dec 2008 21:56:29 -0500
From:	"Mike Snitzer" <snitzer@...il.com>
To:	"Peter Teoh" <htmldeveloper@...il.com>
Cc:	"Rohit Sharma" <imreckless@...il.com>,
	Kernelnewbies <kernelnewbies@...linux.org>,
	ext4 <linux-ext4@...r.kernel.org>
Subject: Re: ext2_block_alloc_info

On Sat, Dec 20, 2008 at 8:25 PM, Peter Teoh <htmldeveloper@...il.com> wrote:
> On Sat, Dec 20, 2008 at 11:43 PM, Rohit Sharma <imreckless@...il.com> wrote:
>> A little confusion.
>>
>> Just refer this structure in linux/ext2_fs_sb.h
>>
>> struct ext2_block_alloc_info {
>>  46        /* information about reservation window */
>>  47        struct ext2_reserve_window_node rsv_window_node;
>>  48        /*
>>  49         * was i_next_alloc_block in ext2_inode_info
>>  50         * is the logical (file-relative) number of the
>>  51         * most-recently-allocated block in this file.
>>  52         * We use this for detecting linearly ascending allocation requests.
>>  53         */
>>  54        __u32                   last_alloc_logical_block;
>
> if i interpret the meaning of "file-relative logical number"
> correctly, and since one-file-one-inode concept, then it means that it
> should mean inode-relative logical block number.
>
>>  55        /*
>>  56         * Was i_next_alloc_goal in ext2_inode_info
>>  57         * is the *physical* companion to i_next_alloc_block.
>>  58         * it the the physical block number of the block which was
>
>> inode1 has logical blocks 0 1 2 , physical 22 23 24
>> inode2 has logical blocks 0 1 2 , physical 34 35 50
>>
>
> as per comment above, the sequence above looks likely, but then this
> is my guess again.

You are correct.  last_alloc_logical_block is used to detect if the
write workload against a given inode is sequential (the current
logical block is last_alloc_logical_block+1).

Mike
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