On Mon, 6 Sep 2010 21:21:28 +0200 Sam Ravnborg <sam@xxxxxxxxxxxx> wrote: > > Comments? > > Looks better but can still use a few improvements. > See below. Thanks for your review and comments.... > > Sam > > > > Thanks, > > NeilBrown > > > > commit e4062735c8f7233923df5858ed20f1278f3ee669 > > Author: NeilBrown <neilb@xxxxxxx> > > Date: Mon Sep 6 14:10:08 2010 +1000 > > > > md: tidy up device searches in read_balance. > > > > We have a pre-increment side-effect in the arg to a macro: > > rcu_dereference > > > > This is poor form and triggers a warning. Rather than just fix that, > > take the opportunity to re-write the code it make it more readable. > > > > Reported-by: Kulikov Vasiliy <segooon@xxxxxxxxx> > > Signed-off-by: NeilBrown <neilb@xxxxxxx> > > > > diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c > > index ad83a4d..e29e13f 100644 > > --- a/drivers/md/raid1.c > > +++ b/drivers/md/raid1.c > > @@ -420,11 +420,13 @@ static void raid1_end_write_request(struct bio *bio, int error) > > static int read_balance(conf_t *conf, r1bio_t *r1_bio) > > { > > const sector_t this_sector = r1_bio->sector; > > - int new_disk = conf->last_used, disk = new_disk; > > - int wonly_disk = -1; > > + int new_disk = -1; > > + int start_disk; > > + int i; > > const int sectors = r1_bio->sectors; > > sector_t new_distance, current_distance; > > mdk_rdev_t *rdev; > > + int choose_first; > > To increase readability the general recommendation is: > 1) Sort variable definitions with the longest first. > 2) Do not assing variables when they are defined, do that on a separate line > below the variable definitions. > With one empty line after variable definitions. > I'm don't really agree with this. I think declaring related variables together is much more important that sorting them by length. I guess it is a very subjective thing. And I think initialising at the point of declaration is often a good idea, though not always. I've moved 'sectors' up near 'this_sector' but nothing else. > > > > rcu_read_lock(); > > /* > > @@ -435,54 +437,35 @@ static int read_balance(conf_t *conf, r1bio_t *r1_bio) > > retry: > > if (conf->mddev->recovery_cp < MaxSector && > > (this_sector + sectors >= conf->next_resync)) { > > - /* Choose the first operational device, for consistancy */ > > - new_disk = 0; > > - > > - for (rdev = rcu_dereference(conf->mirrors[new_disk].rdev); > > - r1_bio->bios[new_disk] == IO_BLOCKED || > > - !rdev || !test_bit(In_sync, &rdev->flags) > > - || test_bit(WriteMostly, &rdev->flags); > > - rdev = rcu_dereference(conf->mirrors[++new_disk].rdev)) { > > - > > - if (rdev && test_bit(In_sync, &rdev->flags) && > > - r1_bio->bios[new_disk] != IO_BLOCKED) > > - wonly_disk = new_disk; > > - > > - if (new_disk == conf->raid_disks - 1) { > > - new_disk = wonly_disk; > > - break; > > - } > > - } > > - goto rb_out; > > + choose_first = 1; > > + start_disk = 0; > > + } else { > > + choose_first = 0; > > + start_disk = conf->last_used; > > } > > > > - > > /* make sure the disk is operational */ > > - for (rdev = rcu_dereference(conf->mirrors[new_disk].rdev); > > - r1_bio->bios[new_disk] == IO_BLOCKED || > > - !rdev || !test_bit(In_sync, &rdev->flags) || > > - test_bit(WriteMostly, &rdev->flags); > > - rdev = rcu_dereference(conf->mirrors[new_disk].rdev)) { > > - > > - if (rdev && test_bit(In_sync, &rdev->flags) && > > - r1_bio->bios[new_disk] != IO_BLOCKED) > > - wonly_disk = new_disk; > > - > > - if (new_disk <= 0) > > - new_disk = conf->raid_disks; > > - new_disk--; > > - if (new_disk == disk) { > > - new_disk = wonly_disk; > > - break; > > + for (i = 0 ; i < conf->raid_disks ; i++) { > > + int disk = start_disk + i; > > + if (disk >= conf->raid_disks) > > + disk -= conf->raid_disks; > 1) Please comment on the purpose of the for loop That would be the comment "make sure the disk is operational" ?? > 2) See comments above aboyt variable definitions Still disagree - sorry. > > > + > > + if (r1_bio->bios[disk] == IO_BLOCKED > > + || !(rdev = rcu_dereference(conf->mirrors[disk].rdev)) > > + || !test_bit(In_sync, &rdev->flags)) > The rather complex expression - which includes a well hidden assignment - > is repeated a few lines later. > Please use a helper function and do not use such hidden assignments. I've moved the assignment out but I don't agree that a helper function is needed. Once must balance the total complexity of the function (which should be kept low) against the cost of having to go look at a separate piece of code to see what a helper function actually does. In this case I think that separating this code out would be 'hiding' rather than 'abstraction'. > > > > + continue; > > + > > + if (test_bit(WriteMostly, &rdev->flags)) { > > + new_disk = disk; > > + continue; > > } > > + new_disk = disk; > > + break; > > } > > > > @@ -491,20 +474,20 @@ static int read_balance(conf_t *conf, r1bio_t *r1_bio) > > if (this_sector == conf->mirrors[new_disk].head_position) > > goto rb_out; > > > > - current_distance = abs(this_sector - conf->mirrors[disk].head_position); > > + current_distance = abs(this_sector > > + - conf->mirrors[new_disk].head_position); > > > > - /* Find the disk whose head is closest */ > > + /* look for a better disk - i.e. head is closer */ > > + start_disk = new_disk; > > + for (i = 1; i < conf->raid_disks; i++) { > > + int disk = start_disk + 1; > > + if (disk >= conf->raid_disks) > > + disk -= conf->raid_disks; > See comments about for loop above. > I also cannot see why we suddenly start with 1 where the other > almost identical for loop starts with 0? > If I wonder then someone else will wonder too => comment please. Before we were finding a working disk. Now were a finding a better disk. First is an absolute statement that needs to consider every device, second is comparative and only needs to consider every other device (... uhm, that doesn't sound right - I don't mean every second device, I mean every device that isn't this one). Suggestions on a comment that would make that clearer? > > > > > - do { > > - if (disk <= 0) > > - disk = conf->raid_disks; > > - disk--; > > - > > - rdev = rcu_dereference(conf->mirrors[disk].rdev); > > - > > - if (!rdev || r1_bio->bios[disk] == IO_BLOCKED || > > - !test_bit(In_sync, &rdev->flags) || > > - test_bit(WriteMostly, &rdev->flags)) > > + if (r1_bio->bios[disk] == IO_BLOCKED > > + || !(rdev = rcu_dereference(conf->mirrors[disk].rdev)) > > + || !test_bit(In_sync, &rdev->flags) > > + || test_bit(WriteMostly, &rdev->flags)) > > continue; > Here the complex expression is repeated - at least almost identical. The 'almost' is key. There are two if conditions that are similar but different. And only two. Factoring parts out would still leave one of them a little complex and would split the task of understanding the condition over two separate parts of program text. I don't think the benefits of a function out-weigh the costs. Thanks, NeilBrown > > > > > if (!atomic_read(&rdev->nr_pending)) { > > @@ -516,11 +499,9 @@ static int read_balance(conf_t *conf, r1bio_t *r1_bio) > > current_distance = new_distance; > > new_disk = disk; > > } > > - } while (disk != conf->last_used); > > + } > > > > rb_out: > > - > > - > > if (new_disk >= 0) { > > rdev = rcu_dereference(conf->mirrors[new_disk].rdev); > > if (!rdev) > > > > Sam -- To unsubscribe from this list: send the line "unsubscribe kernel-janitors" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html