linux-kernel - Re: [PATCH 2/2] fat: optimize fat_count_free

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Date:	Tue, 06 Nov 2007 11:07:12 +0900
From:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] fat: optimize fat_count_free_clusters()

Andrew Morton <akpm@...ux-foundation.org> writes:

>> +/* 128kb is the whole sectors for FAT12 and FAT16 */
>> +#define FAT_READA_SIZE		(128 * 1024)
>> +
>> +static void fat_ent_reada(struct super_block *sb, struct fat_entry *fatent,
>> +			  unsigned long reada_blocks)
>> +{
>> +	struct fatent_operations *ops = MSDOS_SB(sb)->fatent_ops;
>> +	sector_t blocknr;
>> +	int i, offset;
>> +
>> +	ops->ent_blocknr(sb, fatent->entry, &offset, &blocknr);
>> +
>> +	for (i = 0; i < reada_blocks; i++)
>> +		sb_breadahead(sb, blocknr + i);
>> +}
>
> You might find that it's simpler and faster to call
> page_cache_sync_readahead() against sb->s_bdev->bd_inode->i_mapping.
>
> Or maybe not - that requires a struct file_ra_state.  We _used_ to have a
> nice simple read-some-stuff-into-pagecache function which didn't need an
> ra_state but that seems to have disappeared in the various recent readahead
> churn.  Oh well.

Yes. I found it, but I gave up for now by file_ra_state. Also I'd like
to use a large block to read FAT.  I'll rethink this code after large
block was merged.

Thanks.
-- 
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
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