On Tue 20-11-18 17:47:21, Hugh Dickins wrote: > On Tue, 20 Nov 2018, Michal Hocko wrote: > > > From: Michal Hocko <mhocko@xxxxxxxx> > > > > filemap_map_pages takes a speculative reference to each page in the > > range before it tries to lock that page. While this is correct it > > also can influence page migration which will bail out when seeing > > an elevated reference count. The faultaround code would bail on > > seeing a locked page so we can pro-actively check the PageLocked > > bit before page_cache_get_speculative and prevent from pointless > > reference count churn. > > > > Cc: "Kirill A. Shutemov" <kirill@xxxxxxxxxxxxx> > > Suggested-by: Jan Kara <jack@xxxxxxx> > > Signed-off-by: Michal Hocko <mhocko@xxxxxxxx> > > Acked-by: Hugh Dickins <hughd@xxxxxxxxxx> Thanks! > though I think this patch is more useful to the avoid atomic ops, > and unnecessary dirtying of the cacheline, than to avoid the very > transient elevation of refcount, which will not affect page migration > very much. Are you sure it would really be transient? In other words is it possible that the fault around can block migration repeatedly under refault heavy workload? I just couldn't convince myself, to be honest. -- Michal Hocko SUSE Labs
