On Tue, Sep 08 2009, Christoph Hellwig wrote:
> On Sun, Sep 06, 2009 at 08:43:59PM +0200, Jens Axboe wrote:
> > On Fri, Sep 04 2009, Christoph Hellwig wrote:
> > > On Fri, Sep 04, 2009 at 08:53:57AM +0200, Jens Axboe wrote:
> > > > > + if (wbc->sync_mode == WB_SYNC_ALL)
> > > > > + bdi_wait_on_work_clear(&work);
> > > > > }
> > > >
> > > > That doesn't work, you have to wait for on-stack work. So either we just
> > > > punt and not do anything for WB_SYNC_NONE if the allocation fails, or we
> > > > punt to stack and do the wait. Since it's a cleaning action and
> > > > allocation fails, falling back to the stack and waiting seems like the
> > > > most appropriate choice.
> > >
> > > True, the wait needs to be unconditional. Updated version below.
> >
> > (did you forget that patch? it's not there).
>
> Here we go, sorry:
I have applied this to a postmerge writeback branch. I made one change,
though:
> + if (wbc->sync_mode != WB_SYNC_ALL) {
> + struct bdi_work *w = bdi_alloc_work(wbc);
> + if (w) {
> + bdi_queue_work(wbc->bdi, w);
> + return;
> + }
We should make that bdi_queue_work() unconditional, if you want to make
sure that we current thread wakes up and actually flushes some old data
when allocation fails.
void bdi_start_writeback(struct writeback_control *wbc)
{
/*
* WB_SYNC_NONE is opportunistic writeback. If this allocation fails,
* bdi_queue_work() will wake up the thread and flush old data. This
* should ensure some amount of progress in freeing memory.
*/
if (wbc->sync_mode != WB_SYNC_ALL) {
struct bdi_work *w = bdi_alloc_work(wbc);
bdi_queue_work(wbc->bdi, w);
} else {
struct bdi_work work;
bdi_work_init(&work, wbc);
work.state |= WS_ONSTACK;
bdi_queue_work(wbc->bdi, &work);
bdi_wait_on_work_clear(&work);
}
}
--
Jens Axboe
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