6.12-stable review patch. If anyone has any objections, please let me know.
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From: Christoph Hellwig hch@lst.de
[ Upstream commit 7b720c720253e2070459420b2628a7b9ee6733b3 ]
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 holger@applied-asynchrony.com Signed-off-by: Christoph Hellwig hch@lst.de Tested-by: Holger Hoffstätte holger@applied-asynchrony.com Reviewed-by: Hannes Reinecke hare@suse.de Link: https://lore.kernel.org/r/20250424082521.1967286-1-hch@lst.de Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.org --- block/blk-settings.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/block/blk-settings.c b/block/blk-settings.c index 7abf034089cd9..1e63e3dd54402 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; }