From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PULL] vhost: cleanups and fixes Date: Tue, 12 Jun 2018 04:36:54 +0300 Message-ID: <20180612042600-mutt-send-email-mst@kernel.org> References: <20180611192353-mutt-send-email-mst@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Linus Torvalds Cc: KVM list , Network Development , Linux Kernel Mailing List , Bjorn Andersson , Andrew Morton , virtualization List-Id: virtualization@lists.linuxfoundation.org On Mon, Jun 11, 2018 at 11:44:05AM -0700, Linus Torvalds wrote: > On Mon, Jun 11, 2018 at 11:32 AM Linus Torvalds > wrote: > > > > So now we apparently do a GFP_KERNEL allocation insider the mm zone > > lock, which is broken on just _so_ many levels. > > Oh, I see the comment about how it doesn't actually do an allocation > at all because it's a single-entry. > > Still too damn ugly to live, and much too fragile. No way in hell do > we even _hint_ at a GFP_KERNEL when we're inside a context that can't > do any memory allocation at all. > > Plus I'm not convinced it's a "no allocation" path even despite that > comment, because it also does a "dma_map_page()" etc, which can cause > allocations to do the dma mapping thing afaik. No? Well no because DMA is triggered by the IOMMU flag and that is always off for the balloon. But I hear what you are saying about it being fragile. > Maybe there's some reason why that doesn't happen either, but > basically this whole callchain looks *way* to complicated to be used > under a core VM spinlock. > > Linus Maybe it will help to have GFP_NONE which will make any allocation fail if attempted. Linus, would this address your comment? -- MST