Messages in this thread | | | Date | Thu, 04 Jan 2018 13:56:09 +0800 | From | Wei Wang <> | Subject | Re: [PATCH] virtio_balloon: use non-blocking allocation |
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On 01/02/2018 10:50 PM, Tetsuo Handa wrote: > Commit c7cdff0e864713a0 ("virtio_balloon: fix deadlock on OOM") tried to > avoid OOM lockup by moving memory allocations to outside of balloon_lock. > > Now, Wei is trying to allocate far more pages outside of balloon_lock and > some more memory inside of balloon_lock in order to perform efficient > communication between host and guest using scatter-gather API. > > Since pages allocated outside of balloon_lock are not visible to the OOM > notifier path until fill_balloon() holds balloon_lock (and enqueues the > pending pages), allocating more pages than now may lead to unacceptably > premature OOM killer invocation. > > It would be possible to make the pending pages visible to the OOM notifier > path. But there is no need to try to allocate memory so hard from the > beginning. As of commit 18468d93e53b037e ("mm: introduce a common > interface for balloon pages mobility"), it made sense to try allocation > as hard as possible. But after commit 5a10b7dbf904bfe0 ("virtio_balloon: > free some memory from balloon on OOM"), it no longer makes sense to try > allocation as hard as possible, for fill_balloon() will after all have to > release just allocated memory if some allocation request hits the OOM > notifier path. Therefore, this patch disables __GFP_DIRECT_RECLAIM when > allocating memory for inflating the balloon. Then, memory for inflating > the balloon can be allocated inside balloon_lock, and we can release just > allocated memory as needed. > > Also, this patch adds __GFP_NOWARN, for possibility of hitting memory > allocation failure is increased by removing __GFP_DIRECT_RECLAIM, which > might spam the kernel log buffer. At the same time, this patch moves > "puff" messages to outside of balloon_lock, for it is not a good thing to > block the OOM notifier path for 1/5 of a second. (Moreover, it is better > to release the workqueue and allow processing other pending items. But > that change is out of this patch's scope.) > > __GFP_NOMEMALLOC is currently not required because workqueue context > which calls balloon_page_alloc() won't cause __gfp_pfmemalloc_flags() > to return ALLOC_OOM. But since some process context might start calling > balloon_page_alloc() in future, this patch does not remove > __GFP_NOMEMALLOC. > > (Only compile tested. Please do runtime tests before committing.) > > Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> > Cc: Michael S. Tsirkin <mst@redhat.com> > Cc: Wei Wang <wei.w.wang@intel.com> > Cc: Matthew Wilcox <willy@infradead.org> > Cc: Michal Hocko <mhocko@suse.com> > --- > drivers/virtio/virtio_balloon.c | 23 +++++++++++++---------- > mm/balloon_compaction.c | 5 +++-- > 2 files changed, 16 insertions(+), 12 deletions(-) > >
I think it is better to simply make the temporal "LIST_HEAD(pages)" to be visible to oom notify, e.g. make it "struct list_head vb->inflating_pages"
Then we can change virtioballoon_oom_notify():
static int oom_notify() { ... if (*freed != oom_pages && !list_empty(&vb->inflating_pages)) return NOTIFY_BAD;
return NOTIFY_OK; }
virtioballoon_oom_notify() { int ret;
do { ret = oom_notify() } while (ret == NOTIFY_BAD);
return ret; }
I view the above as something "nice to have" (users also have an option to disable F_DEFLATE_ON_OOM, in which case inflated pages are also not released by oom). I can help with this after the "virtio_balloon enhancement" series is done.
Best, Wei
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