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Wong" , Carlos Maiolino , Alexander Viro , Jan Kara Cc: Christoph Hellwig , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, Tal Zussman X-Mailer: b4 0.14.3-dev-d7477 X-Developer-Signature: v=1; a=ed25519-sha256; t=1774464193; l=4705; i=tz2294@columbia.edu; s=20250528; h=from:subject:message-id; bh=SDa413NBu0hIgtXUq9skjN+ObizbWtqbWL36k4Lizgg=; b=rVqeNMymQnbkbA09jjFwfm2fWjVL0ioo1AkqXQ5jcutSE4d0XRwJmwhfNzYW1IkNqhZq2eWVM qHy178rbPMXAdte8ZiWpsnVx+A2KACM+e+P4EnG/GBnw2X8s/dYeyYJ X-Developer-Key: i=tz2294@columbia.edu; a=ed25519; pk=BIj5KdACscEOyAC0oIkeZqLB3L94fzBnDccEooxeM5Y= X-Proofpoint-GUID: DM24Phh7GwerFK_bISURhk1RMyvYeLrS X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMzI1MDE0MiBTYWx0ZWRfXwYN5Pn6t6wTn qkWIk56+dZzC5eSTBhGzoBhjDgugIIm+eu0EsrVErp4cLOywJon/mLq6WAwQjduTfGprF73apZQ JiQc8ZDrGWPuLIcrx7AMUlKJGoy6XPomZ7KjDJ2VXaxXnsBzSEqPgBwt/yNXnTAEMZIJyBS8sBH pBPPKFTK62iFWkpPmc1aAViEXbUfp+zSsdhfxEqDhUTMHVNcw3FAlEPI5WYvlu182m+zCNbk9RW yYLzE3tBNTMz2bfSALYVsgIpspd7bbr9xx6pdkmJoz9NrkJPn7RDvB3lMLjWG5u1HKiNgwnEKVu TyVDHGGTIQaSC0N9gLimk5fE3e/si4+ZJqV9zYX0hbf0D0VOAXayTE9kP9VP/ItfuM6YUv5T9NX jIWcjataE7cBhuXifcxIKfFGS2rPuV+DrODJ8D7aZldBCQ5WK8mth3n5SDpdNi2OL8d75WeYBrW OuZzBrZaN0KvLERv/uw== X-Authority-Analysis: v=2.4 cv=A/th/qWG c=1 sm=1 tr=0 ts=69c437e2 cx=c_pps a=EVbN6Ke/fEF3bsl7X48z0g==:117 a=QOUmeeuX5y9IvSxXHa6D2A==:17 a=IkcTkHD0fZMA:10 a=Yq5XynenixoA:10 a=x7bEGLp0ZPQA:10 a=VkNPw1HP01LnGYTKEx00:22 a=Da8U98TiO7q1upZEImrf:22 a=Qm0qsxP7aFY2tkT6R2MF:22 a=VwQbUJbxAAAA:8 a=tzuM4wBP0trzEmBACekA:9 a=QEXdDO2ut3YA:10 a=a_PwQJl-kcHnX1M80qC6:22 X-Proofpoint-ORIG-GUID: DM24Phh7GwerFK_bISURhk1RMyvYeLrS X-Proofpoint-Virus-Version: vendor=nai engine=6800 definitions=11740 signatures=596818 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 malwarescore=0 spamscore=0 priorityscore=1501 clxscore=1015 impostorscore=10 bulkscore=10 adultscore=0 phishscore=0 lowpriorityscore=10 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2603050001 definitions=main-2603250142 X-Rspamd-Server: rspam12 X-Stat-Signature: fmwzcszt8ktb7gq1hib5xmaspnm93ik5 X-Rspamd-Queue-Id: 73F3840005 X-Rspam-User: X-HE-Tag: 1774467043-856071 X-HE-Meta: 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 5zmEJr8/ 4Ipbz4ZGNKydzF8xwBMi5idlsaWoWoTn3MTwh+8wcRHU6Sl+fbt8ehb/JmrmLBxnoSgtyiSV40A/836TNVgNXlNuer1r1XkgoLcz8kZyKWbmX5c1/cXn/3zVTuQ+mcUNgBkke Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Add support for using RWF_DONTCACHE with block devices. Dropbehind pruning needs to be done in non-IRQ context, but block devices complete writeback in IRQ context. To fix this, we can defer dropbehind invalidation to task context. We introduce a new BIO_COMPLETE_IN_TASK flag that allows the bio submitter to request task-context completion of bi_end_io. When bio_endio() sees this flag in non-task context, it queues the bio to a per-CPU list and schedules a work item to do bio completion. Patch 1 adds the BIO_COMPLETE_IN_TASK infrastructure in the block layer. Patch 2 wires BIO_COMPLETE_IN_TASK into iomap writeback for DONTCACHE folios and removes the DONTCACHE workqueue deferral from XFS. Patch 3 enables RWF_DONTCACHE for block devices, setting BIO_COMPLETE_IN_TASK in submit_bh_wbc() for the CONFIG_BUFFER_HEAD path. This support is useful for databases that operate on raw block devices, among other userspace applications. I tested this (with CONFIG_BUFFER_HEAD=y) for reads and writes on a single block device on a VM, so results may be noisy. Reads were tested on the root partition with a 45GB range (~2x RAM). Writes were tested on a disabled swap parition (~1GB) in a memcg of size 244MB to force reclaim pressure. Results: ===== READS (/dev/nvme0n1p2) ===== sec normal MB/s dontcache MB/s ---- ------------ -------------- 1 1098.6 1609.0 2 1270.3 1506.6 3 1093.3 1576.5 4 1141.8 2393.9 5 1365.3 2793.8 6 1324.6 2065.9 7 879.6 1920.7 8 1434.1 1662.4 9 1184.9 1857.9 10 1166.4 1702.8 11 1161.4 1653.4 12 1086.9 1555.4 13 1198.5 1718.9 14 1111.9 1752.2 ---- ------------ -------------- avg 1173.7 1828.8 (+56%) ==== WRITES (/dev/nvme0n1p3) ===== sec normal MB/s dontcache MB/s ---- ------------ -------------- 1 692.4 9297.7 2 4810.8 9342.8 3 5221.7 2955.2 4 396.7 8488.3 5 7249.2 9249.3 6 6695.4 1376.2 7 122.9 9125.8 8 5486.5 9414.7 9 6921.5 8743.5 10 27.9 8997.8 ---- ------------ -------------- avg 3762.5 7699.1 (+105%) --- Changes in v4: - 1/3: Move dropbehind deferral from folio-level to bio-level using BIO_COMPLETE_IN_TASK, per Matthew and Jan. - 1/3: Work function yields on need_resched() to avoid hogging the CPU, per Jan. - 2/3: New patch. Set BIO_COMPLETE_IN_TASK on iomap writeback bios for DONTCACHE folios, removing the need for XFS-specific workqueue deferral. - 3/3: Set BIO_COMPLETE_IN_TASK in submit_bh_wbc() for buffer_head path. - 3/3: Update commit message to mention CONFIG_BUFFER_HEAD=n path. - Link to v3: https://lore.kernel.org/r/20260227-blk-dontcache-v3-0-cd309ccd5868@columbia.edu Changes in v3: - 1/2: Convert dropbehind deferral to per-CPU folio_batches protected by local_lock using per-CPU work items, to reduce contention, per Jens. - 1/2: Call folio_end_dropbehind_irq() directly from folio_end_writeback(), per Jens. - 1/2: Add CPU hotplug dead callback to drain the departing CPU's folio batch. - 2/2: Introduce block_write_begin_iocb(), per Christoph. - 2/2: Dropped R-b due to changes. - Link to v2: https://lore.kernel.org/r/20260225-blk-dontcache-v2-0-70e7ac4f7108@columbia.edu Changes in v2: - Add R-b from Jan Kara for 2/2. - Add patch to defer dropbehind completion from IRQ context via a work item (1/2). - Add initial performance numbers to cover letter. - Link to v1: https://lore.kernel.org/r/20260218-blk-dontcache-v1-1-fad6675ef71f@columbia.edu --- Tal Zussman (3): block: add BIO_COMPLETE_IN_TASK for task-context completion iomap: use BIO_COMPLETE_IN_TASK for dropbehind writeback block: enable RWF_DONTCACHE for block devices block/bio.c | 84 ++++++++++++++++++++++++++++++++++++++++++++- block/fops.c | 5 +-- fs/buffer.c | 22 ++++++++++-- fs/iomap/ioend.c | 2 ++ fs/xfs/xfs_aops.c | 4 --- include/linux/blk_types.h | 1 + include/linux/buffer_head.h | 3 ++ 7 files changed, 111 insertions(+), 10 deletions(-) --- base-commit: 2961f841b025fb234860bac26dfb7fa7cb0fb122 change-id: 20260218-blk-dontcache-338133dd045e Best regards, -- Tal Zussman