Re: [PATCH 1/1] fat: improve sync performance by grouping writes revised

From: Holden Karau
Date: Tue Oct 31 2006 - 11:47:13 EST


On 10/31/06, Matthew Wilcox <matthew@xxxxxx> wrote:
On Tue, Oct 31, 2006 at 10:03:08AM -0500, Holden Karau wrote:
> @@ -343,52 +344,65 @@ int fat_ent_read(struct inode *inode, st
> return ops->ent_get(fatent);
> }
>
> -/* FIXME: We can write the blocks as more big chunk. */
> -static int fat_mirror_bhs(struct super_block *sb, struct buffer_head **bhs,
> - int nr_bhs)
> +
> +static int fat_mirror_bhs_optw(struct super_block *sb, struct buffer_head **bhs,
> + int nr_bhs , int wait)
> {
> struct msdos_sb_info *sbi = MSDOS_SB(sb);
> - struct buffer_head *c_bh;
> + struct buffer_head *c_bh[nr_bhs*(sbi->fats)];
> int err, n, copy;
>
> + /* Always wait if mounted -o sync */
> + if (sb->s_flags & MS_SYNCHRONOUS )
> + wait = 1;
> err = 0;
> for (copy = 1; copy < sbi->fats; copy++) {
> sector_t backup_fat = sbi->fat_length * copy;
> -
> - for (n = 0; n < nr_bhs; n++) {
> - c_bh = sb_getblk(sb, backup_fat + bhs[n]->b_blocknr);
> - if (!c_bh) {
> + for (n = 0 ; n < nr_bhs ; n++ ) {
> + c_bh[(copy-1)*nr_bhs+n] = sb_getblk(sb, backup_fat + bhs[n]->b_blocknr);
> + if (!c_bh[(copy-1)*nr_bhs+n]) {
> + printk(KERN_CRIT "fat: out of memory while copying backup fat. possible data loss\n");

I don't like that at all.
Not much to be done about that. The amount of memory required is
fairly small, but if its not there its not there.

> err = -ENOMEM;
> goto error;
> }
> - memcpy(c_bh->b_data, bhs[n]->b_data, sb->s_blocksize);
> - set_buffer_uptodate(c_bh);
> - mark_buffer_dirty(c_bh);
> - if (sb->s_flags & MS_SYNCHRONOUS)
> - err = sync_dirty_buffer(c_bh);
> - brelse(c_bh);
> - if (err)
> - goto error;
> + memcpy(c_bh[(copy-1)*nr_bhs+n]->b_data, bhs[n]->b_data, sb->s_blocksize);
> + set_buffer_uptodate(c_bh[(copy-1)*nr_bhs+n]);
> + mark_buffer_dirty(c_bh[(copy-1)*nr_bhs+n]);
> }
> }
> +
> + if (wait) {
> + for (n = 0 ; n < nr_bhs ; n++) {
> + printk("copying to %d to %d\n" ,n, nr_bhs*(sbi->fats-1)+n);

Is this the right version of the patch? The printk should never be left in.
Plus, as far as I can tell, that whole loop is actually just memcpy().
whoops. That was in for debugging, I thought I took that out. The loop
structure is how it was before, but I don't see a way to get rid of
it, do you have an idea?



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