On Tue, Nov 27, 2018 at 02:20:30PM +0100, Vlastimil Babka wrote: > > This patch has a marginal rate on fragmentation rates as it's rare for > > the stall logic to actually trigger but the small stalls can be enough for > > kswapd to catch up. How much that helps is variable but probably worthwhile > > for long-term allocation success rates. It is possible to eliminate > > fragmentation events entirely with tuning due to this patch although that > > would require careful evaluation to determine if it's worthwhile. > > > > Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> > > The gains here are relatively smaller and noisier than for the previous > patches. Also I'm afraid that once antifrag loses against the ultimate > adversary workload (see the "Caching/buffers become useless after some > time" thread), then this might result in adding stalls to a workload > that has no other options but to allocate movable pages from partially > filled unmovable blocks, because that's simply the majority of > pageblocks in the system, and the stalls can't help the situation. If > that proves to be true, we could revert, but then there's the new > user-visible tunable... and that all makes it harder for me to decide > about this patch :) If only we could find out early while this is in > linux-mm/linux-next... > Andrew, would you mind dropping this patch from mmotm please? I think the benefit is marginal relative to the potential loss. If it turns out we ever really do need it then hopefully there will be better data supporting it. Thanks. -- Mel Gorman SUSE Labs
