Messages in this thread |  | | | Date | Mon, 29 Jun 2009 19:34:18 +0200 | | From | Jens Axboe <> | | Subject | Re: [PATCH 2/2] cfq-iosched: get rid of the need for __GFP_FAIL in cfq_find_alloc_queue() |
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On Mon, Jun 29 2009, Jeff Moyer wrote: > Jens Axboe <jens.axboe@oracle.com> writes: > > > On Fri, Jun 26 2009, Jeff Moyer wrote: > >> Jens Axboe <jens.axboe@oracle.com> writes: > >> > >> > 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> > >> > --- > >> > block/cfq-iosched.c | 124 +++++++++++++++++++++++++++----------------------- > >> > 1 files changed, 67 insertions(+), 57 deletions(-) > >> > > >> > diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c > >> > index c760ae7..91e7e0b 100644 > >> > --- a/block/cfq-iosched.c > >> > +++ b/block/cfq-iosched.c > >> > + /* > >> > + * Fallback dummy cfqq for extreme OOM conditions > >> > + */ > >> > + struct cfq_queue oom_cfqq; > >> > >> OK, so you're embedding a cfqq into the cfqd. That's 136 bytes, so I > >> guess that's not too bad. > >> > >> > + /* > >> > + * Our fallback cfqq if cfq_find_alloc_queue() runs into OOM issues. > >> > + * Grab a permanent reference to it, so that the normal code flow > >> > + * will not attempt to free it. > >> > + */ > >> > + cfq_init_cfqq(cfqd, &cfqd->oom_cfqq, 1, 0); > >> > + atomic_inc(&cfqd->oom_cfqq.ref); > >> > + > >> > >> I guess this is so we never try to free it, good. ;) > >> > >> One issue I have with this patch is that, if a task happens to run into > >> this condition, there is no way out. It will always have the oom_cfqq > >> as it's cfqq. Can't we fix that if we recover from the OOM condition? > > > > Yeah, I fixed that about an hour after posting the patches. See: > > > > http://git.kernel.dk/?p=linux-2.6-block.git;a=commit;h=0370bc158cb1d5faa4b8a38c0de3211f0fd5bd64 > > > > I didn't post the 3/2 patch though. > > OK, that looks better. Are you reposting the series, then?
Yeah, I'll fold the last two patches together and repost.
-- Jens Axboe
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