From: Damien Le Moal Date: Mon, 16 Jun 2025 06:28:56 +0000 (+0900) Subject: block: Improve read ahead size for rotational devices X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=459779d04ae8dfd4083679a7bf9d72af165d1023;p=users%2Fjedix%2Flinux-maple.git block: Improve read ahead size for rotational devices For a device that does not advertize an optimal I/O size, the function blk_apply_bdi_limits() defaults to an initial setting of the ra_pages field of struct backing_dev_info to VM_READAHEAD_PAGES, that is, 128 KB. This low I/O size value is far from being optimal for hard-disk devices: when reading files from multiple contexts using buffered I/Os, the seek overhead between the small read commands generated to read-ahead multiple files will significantly limit the performance that can be achieved. This fact applies to all ATA devices as ATA does not define an optimal I/O size and the SCSI SAT specification does not define a default value to expose to the host. Modify blk_apply_bdi_limits() to use a device max_sectors limit to calculate the ra_pages field of struct backing_dev_info, when the device is a rotational one (BLK_FEAT_ROTATIONAL feature is set). For a SCSI disk, this defaults to 2560 KB, which significantly improve performance for buffered reads. Using XFS and sequentially reading randomly selected (large) files stored on a SATA HDD, the maximum throughput achieved with 8 readers reading files with 1MB buffered I/Os increases from 122 MB/s to 167 MB/s (+36%). The improvement is even larger when reading files using 128 KB buffered I/Os, with a throughput increasing from 57 MB/s to 165 MB/s (+189%). Signed-off-by: Damien Le Moal Reviewed-by: John Garry Reviewed-by: Christoph Hellwig Reviewed-by: Martin K. Petersen Link: https://lore.kernel.org/r/20250616062856.1629897-1-dlemoal@kernel.org Signed-off-by: Jens Axboe --- diff --git a/block/blk-settings.c b/block/blk-settings.c index 91449147bae98..608df4674245a 100644 --- a/block/blk-settings.c +++ b/block/blk-settings.c @@ -62,16 +62,24 @@ EXPORT_SYMBOL(blk_set_stacking_limits); void blk_apply_bdi_limits(struct backing_dev_info *bdi, struct queue_limits *lim) { + u64 io_opt = lim->io_opt; + /* * For read-ahead of large files to be effective, we need to read ahead - * at least twice the optimal I/O size. + * at least twice the optimal I/O size. For rotational devices that do + * not report an optimal I/O size (e.g. ATA HDDs), use the maximum I/O + * size to avoid falling back to the (rather inefficient) small default + * read-ahead size. * * There is no hardware limitation for the read-ahead size and the user * might have increased the read-ahead size through sysfs, so don't ever * decrease it. */ + if (!io_opt && (lim->features & BLK_FEAT_ROTATIONAL)) + io_opt = (u64)lim->max_sectors << SECTOR_SHIFT; + bdi->ra_pages = max3(bdi->ra_pages, - lim->io_opt * 2 / PAGE_SIZE, + io_opt * 2 >> PAGE_SHIFT, VM_READAHEAD_PAGES); bdi->io_pages = lim->max_sectors >> PAGE_SECTORS_SHIFT; }