Messages in this thread | | | Date | Mon, 5 Nov 2007 16:49:54 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH 2/2] fat: optimize fat_count_free_clusters() |
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On Mon, 05 Nov 2007 07:09:00 +0900 OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> wrote:
> On large partition, scanning the free clusters is very slow if users > doesn't use "usefree" option. > > For optimizing it, this patch uses sb_breadahead() to read of FAT > sectors. On some user's 15GB partition, this patch improved it very > much (1min => 600ms). > > The following is the result of 2GB partition on my machine. > > without patch: > root@devron (/)# time df -h > /dev/null > > real 0m1.202s > user 0m0.000s > sys 0m0.440s > > with patch: > root@devron (/)# time df -h > /dev/null > > real 0m0.378s > user 0m0.012s > sys 0m0.168s >
Can't complain about that ;)
> --- > > fs/fat/fatent.c | 28 ++++++++++++++++++++++++++++ > 1 file changed, 28 insertions(+) > > diff -puN fs/fat/fatent.c~fat_optimize-count-freeclus fs/fat/fatent.c > --- linux-2.6/fs/fat/fatent.c~fat_optimize-count-freeclus 2007-11-05 06:01:10.000000000 +0900 > +++ linux-2.6-hirofumi/fs/fat/fatent.c 2007-11-05 06:01:10.000000000 +0900 > @@ -590,21 +590,49 @@ error: > > EXPORT_SYMBOL_GPL(fat_free_clusters); > > +/* 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.
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