From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl0-f69.google.com (mail-pl0-f69.google.com [209.85.160.69]) by kanga.kvack.org (Postfix) with ESMTP id 3FCF26B04BE for ; Thu, 4 Jan 2018 00:53:54 -0500 (EST) Received: by mail-pl0-f69.google.com with SMTP id i7so545353plt.3 for ; Wed, 03 Jan 2018 21:53:54 -0800 (PST) Received: from mga07.intel.com (mga07.intel.com. [134.134.136.100]) by mx.google.com with ESMTPS id f4si1805465plb.632.2018.01.03.21.53.52 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 03 Jan 2018 21:53:52 -0800 (PST) Message-ID: <5A4DC1F9.40908@intel.com> Date: Thu, 04 Jan 2018 13:56:09 +0800 From: Wei Wang MIME-Version: 1.0 Subject: Re: [PATCH] virtio_balloon: use non-blocking allocation References: <1514904621-39186-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp> In-Reply-To: <1514904621-39186-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Tetsuo Handa , virtio-dev@lists.oasis-open.org Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Matthew Wilcox , "Michael S. Tsirkin" , Michal Hocko 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 > Cc: Michael S. Tsirkin > Cc: Wei Wang > Cc: Matthew Wilcox > Cc: Michal Hocko > --- > 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org