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Date: Mon, 2 Mar 2020 13:51:50 +0300 From: Konstantin Khlebnikov <khlebnikov@...dex-team.ru> To: Paul Menzel <pmenzel@...gen.mpg.de>, linux-block@...r.kernel.org, Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org Cc: linux-raid@...r.kernel.org, Song Liu <song@...nel.org>, Dmitry Monakhov <dmtrmonakhov@...dex-team.ru> Subject: Re: [PATCH] block: keep bdi->io_pages in sync with max_sectors_kb for stacked devices On 02/03/2020 13.41, Paul Menzel wrote: > Dear Konstantin, > > > Thank you for the patch. > > > On 2020-02-28 15:51, Konstantin Khlebnikov wrote: >> Field bdi->io_pages added in commit 9491ae4aade6 ("mm: don't cap request >> size based on read-ahead setting") removes unneeded split of read requests. >> >> Stacked drivers do not call blk_queue_max_hw_sectors(). Instead they setup > > The verb is spelled with a space *set up*. > >> limits of their devices by blk_set_stacking_limits() + disk_stack_limits(). >> Field bio->io_pages stays zero until user set max_sectors_kb via sysfs. >> >> This patch updates io_pages after merging limits in disk_stack_limits(). >> >> Commit c6d6e9b0f6b4 ("dm: do not allow readahead to limit IO size") fixed >> the same problem for device-mapper devices, this one fixes MD RAIDs. > > Add a Fixes: tag? > > Fixes: 9491ae4aade6 ("mm: don't cap request size based on read-ahead setting") Maybe, but this isn't fatal bug. Just incomplete fix. Same problem exists for non-disk BDIs. I.e. network filesystem must set io_pages manually if doesn't want split read requests. > >> Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru> >> --- >> block/blk-settings.c | 2 ++ >> 1 file changed, 2 insertions(+) >> >> diff --git a/block/blk-settings.c b/block/blk-settings.c >> index c8eda2e7b91e..66c45fd79545 100644 >> --- a/block/blk-settings.c >> +++ b/block/blk-settings.c >> @@ -664,6 +664,8 @@ void disk_stack_limits(struct gendisk *disk, struct block_device *bdev, >> printk(KERN_NOTICE "%s: Warning: Device %s is misaligned\n", >> top, bottom); >> } >> + >> + t->backing_dev_info->io_pages = t->limits.max_sectors >> (PAGE_SHIFT-9); >> } >> EXPORT_SYMBOL(disk_stack_limits); > > Reviewed-by: Paul Menzel <pmenzel@...gen.mpg.de> > > > Kind regards, > > Paul >
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