On Tue, Oct 06, 2020 at 03:07:20PM +0100, Matthew Wilcox wrote: > 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. How far off is this, anyway? I assume it's in line behind the folio series? > 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. /me kinda wonders if THPs arent the better solution for people who want to run large ios. > 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. I can (well, someone can) so I'll talk to you internally about their seeekret reproducer. > https://lore.kernel.org/linux-fsdevel/20200416220130.13343-1-willy@xxxxxxxxxxxxx/ --D
