On Sat 06-11-10 12:12:02, Wu Fengguang wrote:
> On Sat, Nov 06, 2010 at 05:26:23AM +0800, Jan Kara wrote:
>
> > + /*
> > + * In WB_SYNC_ALL mode, we just want to ignore nr_to_write as
> > + * we need to write everything and livelock avoidance is implemented
> > + * differently.
> > + */
> > + if (wbc.sync_mode == WB_SYNC_NONE)
> > + write_chunk = MAX_WRITEBACK_PAGES;
> > + else
> > + write_chunk = LONG_MAX;
>
> This looks like a safe change for .37. I updated the patch on the
> above comment and made no other changes (it seems OK to also remove
> the below line, however that's not the necessary change as a bug fix,
> so I'd rather leave the extra change to the next merge window).
> write_cache_pages():
>
> --> /*
> --> * We stop writing back only if we are not doing
> --> * integrity sync. In case of integrity sync we have to
> --> * keep going until we have written all the pages
> --> * we tagged for writeback prior to entering this loop.
> --> */
> if (--wbc->nr_to_write <= 0 &&
> ==> wbc->sync_mode == WB_SYNC_NONE) {
> done = 1;
> break;
Well, I'd rather leave the test as is. In fact, in my mind-model the
target rather is to completely ignore nr_to_write when we do WB_SYNC_ALL
writeback since obeying it is never what a caller wants to happen...
> + /*
> + * WB_SYNC_ALL mode does livelock avoidance by syncing dirty
> + * inodes/pages in one big loop. Setting wbc.nr_to_write=LONG_MAX
> + * here avoids calling into writeback_inodes_wb() more than once.
Maybe I'd add here:
The intended call sequence for WB_SYNC_ALL writeback is:
> + *
> + * wb_writeback()
> + * writeback_inodes_wb() <== called only once
> + * write_cache_pages() <== called once for each inode
> + * (quickly) tag currently dirty pages
> + * (maybe slowly) sync all tagged pages
> + */
> + if (wbc.sync_mode == WB_SYNC_NONE)
> + write_chunk = MAX_WRITEBACK_PAGES;
> + else
> + write_chunk = LONG_MAX;
> +
Honza
--
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
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