On Thu, 3 Jul 2025 18:34:20 +0100, Matthew Wilcox wrote: > On Thu, Jul 03, 2025 at 06:52:44AM -0700, Christoph Hellwig wrote: > > On Tue, Jul 01, 2025 at 10:48:47PM +0800, alexjlzheng@xxxxxxxxx wrote: > > > From: Jinliang Zheng <alexjlzheng@xxxxxxxxxxx> > > > > > > In the buffer write path, iomap_set_range_uptodate() is called every > > > time iomap_end_write() is called. But if folio_test_uptodate() holds, we > > > know that all blocks in this folio are already in the uptodate state, so > > > there is no need to go deep into the critical section of state_lock to > > > execute bitmap_set(). > > > > > > Although state_lock may not have significant lock contention due to > > > folio lock, this patch at least reduces the number of instructions. > > > > That means the uptodate bitmap is stale in that case. That would > > only matter if we could clear the folio uptodate bit and still > > expect the page content to survive. Which sounds dubious and I could > > not find anything relevant grepping the tree, but I'm adding the > > linux-mm list just in case. > > Once a folio is uptodate, there is no route back to !uptodate without > going through the removal of the folio from the page cache. The read() > path relies on this for example; once it has a refcount on the folio, > and has checked the uptodate bit, it will copy the contents to userspace. I agree, and this aligns with my perspective. Thank you for confirming this. Jinliang Zheng. :)
