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block: never reduce ra_pages in blk_apply_bdi_limits 

JIRA: https://issues.redhat.com/browse/RHEL-87965

commit 7b720c720253e2070459420b2628a7b9ee6733b3
Author: Christoph Hellwig <hch@lst.de>
Date:   Thu Apr 24 10:25:21 2025 +0200

    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 <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: Ming Lei <ming.lei@redhat.com>
This commit is contained in:
Ming Lei 2025-04-24 10:25:21 +02:00
parent c21c8f93b7
commit e06d159a16
1 changed files with 7 additions and 1 deletions
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8
block/blk-settings.c
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@ -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;
}