On Fri 21-10-11 18:40:49, Wu Fengguang wrote:
> Hi Jan,
>
> > How about adding the attached patch to the series? With it applied we
> > would have all busyloop prevention done in the same way.
>
> Sure. It looks good.
Thanks.
> > + pr_warn_ratelimited("mm: Possible busyloop in data writeback "
> > + "(bdi %s nr_pages %ld sync_mode %d kupdate %d "
> > + "background %d)\n",
> > + wb->bdi->name, work->nr_pages, work->sync_mode,
> > + work->for_kupdate, work->for_background);
>
> I'll change the last two fields to the newly introduced writeback "reason":
>
> pr_warn_ratelimited("mm: Possible busyloop in data writeback "
> "(bdi %s nr_pages %ld sync_mode %d reason %s)\n",
> wb->bdi->name, work->nr_pages, work->sync_mode,
> wb_reason_name[work->reason]);
Makes sense. Thanks.
> btw, with the I_SYNC case converted, it's actually no longer necessary
> to keep a standalone b_more_io_wait. It should still be better to keep
> the list and the above error check for catching possible errors and
> the flexibility of adding policies like "don't retry possible blocked
> inodes in N seconds as long as there are other inodes to work with".
>
> The below diff only intends to show the _possibility_ to remove
> b_more_io_wait:
Good observation. So should we introduce b_more_io_wait in the end? We
could always introduce it when the need for some more complicated policy
comes...
Honza
>
> --- linux-next.orig/fs/fs-writeback.c 2011-10-21 18:25:25.000000000 +0800
> +++ linux-next/fs/fs-writeback.c 2011-10-21 18:27:41.000000000 +0800
> @@ -235,20 +235,7 @@ static void requeue_io(struct inode *ino
> list_move(&inode->i_wb_list, &wb->b_more_io);
> }
>
> -/*
> - * The inode should be retried in an opportunistic way.
> - *
> - * The only difference between b_more_io and b_more_io_wait is:
> - * wb_writeback() won't quit as long as b_more_io is not empty. When
> - * wb_writeback() quit on empty b_more_io and non-empty b_more_io_wait,
> - * the kupdate work will wakeup more frequently to retry the inodes in
> - * b_more_io_wait.
> - */
> -static void requeue_io_wait(struct inode *inode, struct bdi_writeback *wb)
> -{
> - assert_spin_locked(&wb->list_lock);
> - list_move(&inode->i_wb_list, &wb->b_more_io_wait);
> -}
> +#define requeue_io_wait(inode, wb) requeue_io(inode, wb)
>
> static void inode_sync_complete(struct inode *inode)
> {
> @@ -798,21 +785,8 @@ static long wb_writeback(struct bdi_writ
> * mean the overall work is done. So we keep looping as long
> * as made some progress on cleaning pages or inodes.
> */
> - if (progress)
> - continue;
> - /*
> - * No more inodes for IO, bail
> - */
> - if (list_empty(&wb->b_more_io))
> + if (!progress)
> break;
> - /*
> - * Nothing written but some inodes were moved to b_more_io.
> - * This should not happen as we can easily busyloop.
> - */
> - pr_warn_ratelimited("mm: Possible busyloop in data writeback "
> - "(bdi %s nr_pages %ld sync_mode %d reason %s)\n",
> - wb->bdi->name, work->nr_pages, work->sync_mode,
> - wb_reason_name[work->reason]);
> }
> spin_unlock(&wb->list_lock);
>
> Thanks,
> Fengguang
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