Messages in this thread | | | From | Jeff Moyer <> | Subject | Re: [PATCH 2/2] cfq-iosched: get rid of the need for __GFP_FAIL in cfq_find_alloc_queue() | Date | Mon, 29 Jun 2009 13:44:07 -0400 |
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Jens Axboe <jens.axboe@oracle.com> writes:
> 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.
When you do, you can add my:
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Cheers, Jeff
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