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([2620:10d:c090:400::5:32c6]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-1f44c96f26bsm346775ad.127.2024.05.23.14.17.58 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 23 May 2024 14:17:59 -0700 (PDT) Message-ID: <359117d3-20e3-4c1b-a426-8ec1391ffec4@kernel.dk> Date: Thu, 23 May 2024 15:17:57 -0600 Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/filemap: invalidating pages is still necessary when io with IOCB_NOWAIT To: Matthew Wilcox , Andrew Morton Cc: linux-kernel@vger.kernel.org, Goldwyn Rodrigues , Christoph Hellwig , Jan Kara , linux-fsdevel@vger.kernel.org References: <20240513132339.26269-1-liuwei09@cestc.cn> <20240523130802.730d2790b8e5f691871575c0@linux-foundation.org> Content-Language: en-US From: Jens Axboe In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 5/23/24 3:11 PM, Matthew Wilcox wrote: > On Thu, May 23, 2024 at 01:08:02PM -0700, Andrew Morton wrote: >> On Mon, 13 May 2024 21:23:39 +0800 Liu Wei wrote: >> >>> After commit (6be96d3ad3 fs: return if direct I/O will trigger writeback), >>> when we issuing AIO with direct I/O and IOCB_NOWAIT on a block device, the >>> process context will not be blocked. >>> >>> However, if the device already has page cache in memory, EAGAIN will be >>> returned. And even when trying to reissue the AIO with direct I/O and >>> IOCB_NOWAIT again, we consistently receive EAGAIN. >>> >>> Maybe a better way to deal with it: filemap_fdatawrite_range dirty pages >>> with WB_SYNC_NONE flag, and invalidate_mapping_pages unmapped pages at >>> the same time. >> >> Can't userspace do this? If EAGAIN, sync the fd and retry the IO? > > I don't think that it can, because the pages will still be there, even > if now clean? I think the idea was to punt to a worker thread which > could sleep and retry without NOWAIT. But let's see what someone > involved in this patch has to say about the intent. Right, the idea is that if you get -EAGAIN, a non-blocking attempt wasn't possible. You'd need to retry from somewhere where you CAN block. Any issuer very much can do that, whether it's in-kernel or not. It'd be somewhat fragile to make assumptions on what can cause the -EAGAIN and try to rectify them, and then try again with IOCB_NOWAIT. -- Jens Axboe