Re: [PATCH 0/6] More graceful flusher thread memory reclaim wakeup

[John Stoffel]

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.

John