On Mon, Oct 17, 2022 at 12:43 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > > On Mon, Oct 17, 2022 at 12:37:48PM -0700, Vishal Moola wrote: > > On Mon, Oct 17, 2022 at 9:56 AM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > > > > > > On Mon, Oct 17, 2022 at 09:17:59AM -0700, Vishal Moola (Oracle) wrote: > > > > +++ b/mm/shmem.c > > > > @@ -932,21 +932,18 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend, > > > > > > > > folio_batch_init(&fbatch); > > > > index = start; > > > > - while (index < end && find_lock_entries(mapping, index, end - 1, > > > > + while (index < end && find_lock_entries(mapping, &index, end - 1, > > > > > > Sorry for not spotting this in earlier revisions, but this is wrong. > > > Before, find_lock_entries() would go up to (end - 1) and then the > > > index++ at the end of the loop would increment index to "end", causing > > > the loop to terminate. Now we don't increment index any more, so the > > > condition is wrong. > > > > The condition is correct. Index maintains the exact same behavior. > > If a find_lock_entries() finds a folio, index is set to be directly after > > the last page in that folio, or simply incrementing for a value entry. > > The only time index is not changed at all is when find_lock_entries() > > finds no folios, which is the same as the original behavior as well. > > Uh, right. I had the wrong idea in my head that index wouldn't increase > past end-1, but of course it can. > > > > I suggest just removing the 'index < end" half of the condition. > > > > I hadn't thought about it earlier but this index < end check seems > > unnecessary anyways. If index > end then find_lock_entries() > > shouldn't find any folios which would cause the loop to terminate. > > > > I could send an updated version getting rid of the "index < end" > > condition as well if you would like? > > Something to consider is that if end is 0 then end-1 is -1, which is > effectively infinity, and we'll do the wrong thing? So maybe just > leave it alone, and go with v3 as-is? Yeah in that case find_lock_entries() would definitely do the wrong thing. I was thinking the "end-1" could be replaced with "end" as well as removing the "index < end". But that would change the behavior of the function(s) to now deal with end inclusive rather than exclusive which may or may not be problematic. Considering that I don't see any compelling reason to eliminate the "index < end" condition. I say we go with v3 as-is if there are no problems.
