From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Sat, 15 Dec 2018 06:38:24 -0800 From: Matthew Wilcox To: Hou Tao Cc: phillip@squashfs.org.uk, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH] squashfs: enable __GFP_FS in ->readpage to prevent hang in mem alloc Message-ID: <20181215143824.GJ10600@bombadil.infradead.org> References: <20181204020840.49576-1-houtao1@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181204020840.49576-1-houtao1@huawei.com> Sender: owner-linux-mm@kvack.org List-ID: On Tue, Dec 04, 2018 at 10:08:40AM +0800, Hou Tao wrote: > There is no need to disable __GFP_FS in ->readpage: > * It's a read-only fs, so there will be no dirty/writeback page and > there will be no deadlock against the caller's locked page > * It just allocates one page, so compaction will not be invoked > * It doesn't take any inode lock, so the reclamation of inode will be fine > > And no __GFP_FS may lead to hang in __alloc_pages_slowpath() if a > squashfs page fault occurs in the context of a memory hogger, because > the hogger will not be killed due to the logic in __alloc_pages_may_oom(). I don't understand your argument here. There's a comment in __alloc_pages_may_oom() saying that we _should_ treat GFP_NOFS specially, but we currently don't. /* * XXX: GFP_NOFS allocations should rather fail than rely on * other request to make a forward progress. * We are in an unfortunate situation where out_of_memory cannot * do much for this context but let's try it to at least get * access to memory reserved if the current task is killed (see * out_of_memory). Once filesystems are ready to handle allocation * failures more gracefully we should just bail out here. */ What problem are you actually seeing?