On Mon, Oct 05, 2020 at 08:55:37PM -0700, Darrick J. Wong wrote: > On Mon, Oct 05, 2020 at 11:21:02AM -0400, Brian Foster wrote: > > We've had reports of soft lockup warnings in the iomap ioend > > completion path due to very large bios and/or bio chains. Divert any > > ioends with 256k or more pages to process to the workqueue so > > completion occurs in non-atomic context and can reschedule to avoid > > soft lockup warnings. > > Hmmmm... is there any way we can just make end_page_writeback faster? There are ways to make it faster. I don't know if they're a "just" solution ... 1. We can use THPs. That will reduce the number of pages being operated on. I hear somebody might have a patch set for that. Incidentally, this patch set will clash with the THP patchset, so one of us is going to have to rebase on the other's work. Not a complaint, just acknowledging that some coordination will be needed for the 5.11 merge window. 2. We could create end_writeback_pages(struct pagevec *pvec) which calls a new test_clear_writeback_pages(pvec). That could amortise taking the memcg lock and finding the lruvec and taking the mapping lock -- assuming these pages are sufficiently virtually contiguous. It can definitely amortise all the statistics updates. 3. We can make wake_up_page(page, PG_writeback); more efficient. If you can produce this situation on demand, I had a patch for that which languished due to lack of interest. https://lore.kernel.org/linux-fsdevel/20200416220130.13343-1-willy@xxxxxxxxxxxxx/
