From: Christoph Hellwig Date: Thu, 24 Apr 2025 08:25:21 +0000 (+0200) Subject: block: never reduce ra_pages in blk_apply_bdi_limits X-Git-Tag: v6.15-rc4~18^2~6 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=7b720c720253e2070459420b2628a7b9ee6733b3;p=thirdparty%2Flinux.git block: never reduce ra_pages in blk_apply_bdi_limits When the user increased the read-ahead size through sysfs this value currently get lost if the device is reprobe, including on a resume from suspend. As there is no hardware limitation for the read-ahead size there is no real need to reset it or track a separate hardware limitation like for max_sectors. This restores the pre-atomic queue limit behavior in the sd driver as sd did not use blk_queue_io_opt and thus never updated the read ahead size to the value based of the optimal I/O, but changes behavior for all other drivers. As the new behavior seems useful and sd is the driver for which the readahead size tweaks are most useful that seems like a worthwhile trade off. Fixes: 804e498e0496 ("sd: convert to the atomic queue limits API") Reported-by: Holger Hoffstätte Signed-off-by: Christoph Hellwig Tested-by: Holger Hoffstätte Reviewed-by: Hannes Reinecke Link: https://lore.kernel.org/r/20250424082521.1967286-1-hch@lst.de Signed-off-by: Jens Axboe --- diff --git a/block/blk-settings.c b/block/blk-settings.c index 6b2dbe645d23a..4817e7ca03f83 100644 --- a/block/blk-settings.c +++ b/block/blk-settings.c @@ -61,8 +61,14 @@ void blk_apply_bdi_limits(struct backing_dev_info *bdi, /* * For read-ahead of large files to be effective, we need to read ahead * at least twice the optimal I/O 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. */ - bdi->ra_pages = max(lim->io_opt * 2 / PAGE_SIZE, VM_READAHEAD_PAGES); + bdi->ra_pages = max3(bdi->ra_pages, + lim->io_opt * 2 / PAGE_SIZE, + VM_READAHEAD_PAGES); bdi->io_pages = lim->max_sectors >> PAGE_SECTORS_SHIFT; }