On Mon, Feb 03, 2014 at 02:32:45PM -0700, Andreas Dilger wrote:
> On Feb 1, 2014, at 3:37 AM, Darrick J. Wong <darrick.wong@xxxxxxxxxx> wrote:
> > This patch adds to libext2fs the ability to pre-fetch metadata
> > into the page cache in the hopes of speeding up libext2fs' clients.
> > There are two new library functions -- the first allows a client to
> > readahead a list of blocks, and the second is a helper function that
> > uses that first mechanism to load group data (bitmaps, inode tables).
> >
> > e2fsck will employ both of these methods to speed itself up.
> >
> > diff --git a/lib/ext2fs/readahead.c b/lib/ext2fs/readahead.c
> > new file mode 100644
> > index 0000000..05f6135
> > --- /dev/null
> > +++ b/lib/ext2fs/readahead.c
> > +errcode_t ext2fs_readahead(ext2_filsys fs, int flags, dgrp_t start,
> > + dgrp_t ngroups)
> > +{
> > +
> > + for (i = start; i < end; i++) {
> > + if ((flags & EXT2FS_READ_ITABLE) &&
> > + ext2fs_bg_free_inodes_count(fs, i) <
> > + fs->super->s_inodes_per_group) {
> > + super = ext2fs_inode_table_loc(fs, i);
> > + err = ext2fs_add_dir_block2(dblist, 0, super,
> > + fs->inode_blocks_per_group);
>
> This prefetches all of the inode table blocks, when it could instead
> just prefetch the in-use blocks using:
>
> if ((flags & EXT2FS_READ_ITABLE) &&
> ext2fs_bg_itable_unused(fs, i) <
> fs->inode_blocks_per_group))
> err = ext2fs_add_dir_block2(dblist, 0, super,
> fs->inode_blocks_per_group -
> ext2fs_bg_itable_unused(fs, i));
I think you need to convert ext2fs_bg_itable_unused() to blocks there, but
point taken. Actually, the first insane-o patch had this, but I forgot it when
writing up the second version.
> If there is corruption in the filesystem and the "unused" blocks need
> to be read later it is probably more than offset by not reading those
> actually unused blocks for the rest of the time.
<shrug> I'm not particularly concerned about less than optimal IO throughput on
broken filesystems.
--D
>
>
> Cheers, Andreas
>
>
>
>
>
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
