Messages in this thread | | | Subject | Re: [PATCH] virtio_balloon: use non-blocking allocation | From | Tetsuo Handa <> | Date | Wed, 31 Jan 2018 20:13:26 +0900 |
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Michael S. Tsirkin wrote: > On Tue, Jan 02, 2018 at 11:50:21PM +0900, 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"), > > However, please not that this behavious is optional. > Can you keep the current behaviour when deflate on OOM is disabled?
I can, for passing a flag to balloon_page_alloc() will do it.
But do we really prefer behavior up to comment 27 of https://bugzilla.redhat.com/show_bug.cgi?id=1525356 ?
> > > > 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.) > > You will have to find someone to test it.
I don't have machines with much memory.
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