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bh=jdHAIpfWqWHafM+znmNZIJaMTPI5wENHSEaIJXcuW90=; b=lzc8Tv+KHTfVdvGvze10XxjrSIZ2hhn2empYYzUDdE75SNQE02xNXyArA67XKXkpCi XyfSZKqmv7qnp7Dkpag7gxSoaDw0/Iy+or3CUVLfFK5vlOUIZZ8pW9Li24pMm8Ms9zsX PglCBw2IjtMHrfVNBe+ShE+QGuoWgknhU3avxtmOWLmFiSRMBJuPV6kkCvnv6ePSA/Vt q6NddfMfeDDgsz+zavqtQ+GXV2FNyC8Z2ptPlVg8VOii/bwQSBPg2AsZniiwMlnZAH0Y fMg891nDY8fS0FSYAf9qn15QJKMuHnZ5TEpflayJ0VNhQZOTUbUw+RjPZRuc+srGtq1G aGpQ== X-Gm-Message-State: AOAM532Y8RzXc2xvh9IXUdXRU9xFWJfZAtpHpGoLqAonFZAm2WENC2dg disrqIiy+JUkZNUNo7V4cFBQlPKNu90ligq07+MSPjDKKK/o4IMwbqSsAcvXea0VaCKEwI2K4ij hK7wpNoDRWus+54sUIsr8BZstn0c= X-Received: by 2002:a4a:868a:: with SMTP id x10mr47045442ooh.31.1594132231282; Tue, 07 Jul 2020 07:30:31 -0700 (PDT) X-Google-Smtp-Source: ABdhPJxkyrmC9YyVoZKCHhEbKVmEbE0QU21dPZEuBspnOoCY6PvjRo2XRprybq1+LMm+sMOQeYKXQRvYJk4hHGy4wPw= X-Received: by 2002:a4a:868a:: with SMTP id x10mr47045402ooh.31.1594132230968; Tue, 07 Jul 2020 07:30:30 -0700 (PDT) MIME-Version: 1.0 References: <20200702165120.1469875-1-agruenba@redhat.com> <20200702165120.1469875-3-agruenba@redhat.com> In-Reply-To: From: Andreas Gruenbacher Date: Tue, 7 Jul 2020 16:30:19 +0200 Message-ID: Subject: Re: [RFC 2/4] fs: Add IOCB_NOIO flag for generic_file_read_iter To: Linus Torvalds Cc: Matthew Wilcox , Dave Chinner , linux-fsdevel , Linux-MM , Linux Kernel Mailing List Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=agruenba@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: DE68E14502 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam05 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Jul 2, 2020 at 8:06 PM Linus Torvalds wrote: > On Thu, Jul 2, 2020 at 9:51 AM Andreas Gruenbacher wrote: > > Add an IOCB_NOIO flag that indicates to generic_file_read_iter that it > > shouldn't trigger any filesystem I/O for the actual request or for > > readahead. This allows to do tentative reads out of the page cache as > > some filesystems allow, and to take the appropriate locks and retry the > > reads only if the requested pages are not cached. > > This looks sane to me, except for this part: > > if (!PageUptodate(page)) { > > - if (iocb->ki_flags & IOCB_NOWAIT) { > > + if (iocb->ki_flags & (IOCB_NOWAIT | IOCB_NOIO)) { > > put_page(page); > > goto would_block; > > } > > This path doesn't actually initiate reads at all - it waits for > existing reads to finish. > > So I think it should only check for IOCB_NOWAIT. It turns out that label readpage is reachable from here via goto page_not_up_to_date / goto page_not_up_to_date_locked. So IOCB_NOIO needs to be checked somewhere. I'll send an update. Andreas