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Fri, 20 May 2022 18:29:21 +0000 Received: from MW4PR15MB4410.namprd15.prod.outlook.com ([fe80::606b:25cf:e181:9f99]) by MW4PR15MB4410.namprd15.prod.outlook.com ([fe80::606b:25cf:e181:9f99%4]) with mapi id 15.20.5273.016; Fri, 20 May 2022 18:29:21 +0000 Message-ID: Date: Fri, 20 May 2022 11:29:18 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:91.0) Gecko/20100101 Thunderbird/91.8.0 Subject: Re: [RFC PATCH v3 04/18] iomap: Add async buffered write support Content-Language: en-US To: Christoph Hellwig Cc: io-uring@vger.kernel.org, kernel-team@fb.com, linux-mm@kvack.org, linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, david@fromorbit.com, jack@suse.cz References: <20220518233709.1937634-1-shr@fb.com> <20220518233709.1937634-5-shr@fb.com> From: Stefan Roesch In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: BYAPR03CA0010.namprd03.prod.outlook.com (2603:10b6:a02:a8::23) To MW4PR15MB4410.namprd15.prod.outlook.com (2603:10b6:303:bf::10) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: ab4a5d8a-a429-4b9d-89c1-08da3a8ea88f X-MS-TrafficTypeDiagnostic: BYAPR15MB3477:EE_ X-Microsoft-Antispam-PRVS: X-FB-Source: Internal X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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The support is focused >> on the changes necessary to support XFS with iomap. >> >> Support for other filesystems might require additional changes. > > What would those other changes be? Inline data support should not > matter here, so I guess it is buffer_head support? Please spell out > the actual limitations instead of the use case. Preferably including > asserts in the code to catch the case of a file system trying to use > the now supported cases. > I was only trying to make the point that I haven't enabled this on other filesystems than XFS. Removing the statement as it causes confusion. >> >> Signed-off-by: Stefan Roesch >> --- >> fs/iomap/buffered-io.c | 18 ++++++++++++++++++ >> 1 file changed, 18 insertions(+) >> >> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c >> index 6b06fd358958..b029e2b10e07 100644 >> --- a/fs/iomap/buffered-io.c >> +++ b/fs/iomap/buffered-io.c >> @@ -580,12 +580,18 @@ static int __iomap_write_begin(const struct iomap_iter *iter, loff_t pos, >> size_t from = offset_in_folio(folio, pos), to = from + len; >> size_t poff, plen; >> gfp_t gfp = GFP_NOFS | __GFP_NOFAIL; >> + bool no_wait = (iter->flags & IOMAP_NOWAIT); >> + >> + if (no_wait) > > Does thi flag really buy us anything? My preference woud be to see > the IOMAP_NOWAIT directy as that is easier for me to read than trying to > figure out what no_wait actually means. > Removed the no_wait variable and instead used the flag check directly in the code. >> + gfp = GFP_NOWAIT; >> >> if (folio_test_uptodate(folio)) >> return 0; >> folio_clear_error(folio); >> >> iop = iomap_page_create_gfp(iter->inode, folio, nr_blocks, gfp); > > And maybe the btter iomap_page_create inteface would be one that passes > the flags so that we can centralize the gfp_t selection. > >> @@ -602,6 +608,8 @@ static int __iomap_write_begin(const struct iomap_iter *iter, loff_t pos, >> if (WARN_ON_ONCE(iter->flags & IOMAP_UNSHARE)) >> return -EIO; >> folio_zero_segments(folio, poff, from, to, poff + plen); >> + } else if (no_wait) { >> + return -EAGAIN; >> } else { >> int status = iomap_read_folio_sync(block_start, folio, >> poff, plen, srcmap); > > That's a somewhat unnatural code flow. I'd much prefer: > I made the below change. > } else { > int status; > > if (iter->flags & IOMAP_NOWAIT) > return -EAGAIN; > iomap_read_folio_sync(block_start, folio, > poff, plen, srcmap); > > Or maybe even pass the iter to iomap_read_folio_sync and just do the > IOMAP_NOWAIT check there.