Re: [PATCH 2/2] cfq-iosched: get rid of the need for __GFP_FAIL in cfq_find_alloc_queue()

Jens Axboe
2009-07-01T09:32:42Z

On Wed, Jul 01 2009, Shan Wei wrote:
> Jens Axboe said:
> > Setup an emergency fallback cfqq that we allocate at IO scheduler init
> > time. If the slab allocation fails in cfq_find_alloc_queue(), we'll just
> > punt IO to that cfqq instead. This ensures that cfq_find_alloc_queue()
> > never fails without having to ensure free memory.
> >
> > Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
> > ---
> >
> > @@ -1740,11 +1745,8 @@ cfq_get_queue(struct cfq_data *cfqd, int is_sync, struct io_context *ioc,
> > cfqq = *async_cfqq;
> > }
> >
> > - if (!cfqq) {
> > + if (!cfqq)
> > cfqq = cfq_find_alloc_queue(cfqd, is_sync, ioc, gfp_mask);
> > - if (!cfqq)
> > - return NULL;
> > - }
>
> I jsut reviewed the code and found that the check of cfqq is also redundant
> after doing cfq_get_queue() in cfq_set_request.
>
> The patch is based on Linus's main tree.

It's not redundant in Linus' tree, cfq_get_queue() can return NULL for
!= __GFP_WAIT.

>
> Signed-off-by: Shan Wei <shanwei@cn.fujitsu.com>
> ---
> block/cfq-iosched.c | 4 ----
> 1 files changed, 0 insertions(+), 4 deletions(-)
>
> diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
> index 833ec18..c373237 100644
> --- a/block/cfq-iosched.c
> +++ b/block/cfq-iosched.c
> @@ -2307,10 +2307,6 @@ cfq_set_request(struct request_queue *q, struct request *rq, gfp_t gfp_mask)
> cfqq = cic_to_cfqq(cic, is_sync);
> if (!cfqq) {
> cfqq = cfq_get_queue(cfqd, is_sync, cic->ioc, gfp_mask);
> -
> - if (!cfqq)
> - goto queue_fail;
> -
> cic_set_cfqq(cic, cfqq, is_sync);
> }
>

--
Jens Axboe