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SubjectRe: [PATCH 1/1] fat: improve sync performance by grouping writes revised again
On 11/1/06, Jörn Engel <joern@wohnheim.fh-wedel.de> wrote:
> On Wed, 1 November 2006 11:17:50 -0500, Holden Karau wrote:
> > + c_bh = kmalloc(nr_bhs*(sbi->fats) , GFP_KERNEL);
> > + if (NULL == c_bh) {
> > + printk(KERN_CRIT "not enough memory to store pointers to FAT blocks, will not sync. Possible data loss\n");
> > + err = -ENOMEM;
> > + goto error;
> > + }
>
> o I personally hate Yoda code ("Null the pointer is not, young Jedi").
> o Old code simply returned -ENOMEM without printk. Assuming this was
> sufficient before, the printk can be dropped.
Ok, I'll drop the printk
> o Some people prefer assigning err outside the condition. It is
> supposed to give slightly better code on i386, iirc.
>
> Result would be something like:
> c_bh = kmalloc(...
> err = -ENOMEM;
> if (!c_bh)
> goto error;
That wouldn't work so well since we always return err, and possibly
slightly better code for i386 doesn't seem all that worth it.
>
> > + for (n = 0 ; n < nr_bhs ; n++ ) {
> > + c_bh[(copy-1)*nr_bhs+n] = sb_getblk(sb, backup_fat + bhs[n]->b_blocknr);
> > + /* If there is not enough memory, fall back to the old system */
> > + if (!c_bh[(copy-1)*nr_bhs+n]) {
> > + printk("fat: not enough memory for all blocks , syncing at %d\n" ,(copy-1)*nr_bhs+n);
>
> Whether this printk makes sense, I cannot tell.
I suppose I might as well drop it.
>
> > + fat_sync_bhs_optw( c_bh+i , (copy-1)*nr_bhs+n-i-1 , wait );
> > + /* Free the now sync'd blocks */
> > + for (; i < (copy-1)*nr_bhs+n ; i++)
> > + brelse(c_bh[i]);
> > + /* We try the same block again */
> > + 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:not enough memory for block after existing blocks released. Possible data loss.\n");
Based on the same reasoning you provided, I should probably drop this one too.
> > + err = -ENOMEM;
> > + goto error;
> > + }
>
> As above.
I'll drop the printk, but the same holds true about err
>
> > error:
> > + if (NULL != c_bh) {
> > + kfree(c_bh);
> > + }
>
> kfree(NULL) works just fine. You can remove the condition.
Thanks, I should have checked that :-)
>
> > +int fat_sync_bhs_optw(struct buffer_head **bhs, int nr_bhs ,int wait)
> > {
> > int i, err = 0;
> >
> > ll_rw_block(SWRITE, nr_bhs, bhs);
> > - for (i = 0; i < nr_bhs; i++) {
> > - wait_on_buffer(bhs[i]);
> > - if (buffer_eopnotsupp(bhs[i])) {
> > - clear_buffer_eopnotsupp(bhs[i]);
> > - err = -EOPNOTSUPP;
> > - } else if (!err && !buffer_uptodate(bhs[i]))
> > - err = -EIO;
> > + if (wait) {
> > + for (i = 0; i < nr_bhs; i++) {
> > + wait_on_buffer(bhs[i]);
> > + if (buffer_eopnotsupp(bhs[i])) {
> > + clear_buffer_eopnotsupp(bhs[i]);
> > + err = -EOPNOTSUPP;
> > + } else if (!err && !buffer_uptodate(bhs[i]))
> > + err = -EIO;
> > + }
> > }
> > +
> > return err;
> > }
>
> You could keep the old indentation if your condition was changed to
>
> if (!wait)
> return 0;
Sounds good.
>
> Jörn
>
> --
> You can take my soul, but not my lack of enthusiasm.
> -- Wally
>


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