Matthew Wilcox <willy@xxxxxxxxxxxxx> writes: > On Sun, Aug 30, 2020 at 09:59:41AM +0900, OGAWA Hirofumi wrote: >> On one system, there was bdi->io_pages==0. This seems to be the bug of >> a driver somewhere, and should fix it though. Anyway, it is better to >> avoid the divide-by-zero Oops. >> >> So this check it. >> >> Signed-off-by: OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx> >> Cc: <stable@xxxxxxxxxxxxxxx> >> --- >> fs/fat/fatent.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/fs/fat/fatent.c b/fs/fat/fatent.c >> index f7e3304..98a1c4f 100644 >> --- a/fs/fat/fatent.c 2020-08-30 06:52:47.251564566 +0900 >> +++ b/fs/fat/fatent.c 2020-08-30 06:54:05.838319213 +0900 >> @@ -660,7 +660,7 @@ static void fat_ra_init(struct super_blo >> if (fatent->entry >= ent_limit) >> return; >> >> - if (ra_pages > sb->s_bdi->io_pages) >> + if (sb->s_bdi->io_pages && ra_pages > sb->s_bdi->io_pages) >> ra_pages = rounddown(ra_pages, sb->s_bdi->io_pages); > > Wait, rounddown? ->io_pages is supposed to be the maximum number of > pages to readahead. Shouldn't this be max() instead of rounddown()? Hm, io_pages is limited by driver setting too, and io_pages can be lower than ra_pages, e.g. usb storage. Assuming ra_pages is user intent of readahead window. So if io_pages is lower than ra_pages, this try ra_pages to align of io_pages chunk, but not bigger than ra_pages. Because if block layer splits I/O requests to hard limit, then I/O is not optimal. So it is intent, I can be misunderstanding though. Thanks. -- OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx>
