On 09/20/2017 01:29 PM, John Stoffel wrote: > On Tue, Sep 19, 2017 at 01:53:01PM -0600, Jens Axboe wrote: >> We've had some issues with writeback in presence of memory reclaim >> at Facebook, and this patch set attempts to fix it up. The real >> functional change is the last patch in the series, the first 5 are >> prep and cleanup patches. >> >> The basic idea is that we have callers that call >> wakeup_flusher_threads() with nr_pages == 0. This means 'writeback >> everything'. For memory reclaim situations, we can end up queuing >> a TON of these kinds of writeback units. This can cause softlockups >> and further memory issues, since we allocate huge amounts of >> struct wb_writeback_work to handle this writeback. Handle this >> situation more gracefully. > > This looks nice, but do you have any numbers to show how this improves > things? I read the patches, but I'm not strong enough to comment on > them at all. But I am interested in how this improves writeback under > pressure, if at all. Writeback should be about the same, it's mostly about preventing softlockups and excessive memory usage, under conditions where we are actively trying to reclaim/clean memory. It was bad enough to cause softlockups for writeback work processing, while the pending writeback work units grew to insane lengths. -- Jens Axboe
