On 11/29/22 16:17, Mel Gorman wrote: > From: NeilBrown <neilb@xxxxxxx> > > __GFP_ATOMIC serves little purpose. Its main effect is to set > ALLOC_HARDER which adds a few little boosts to increase the chance of an > allocation succeeding, one of which is to lower the water-mark at which it > will succeed. > > It is *always* paired with __GFP_HIGH which sets ALLOC_HIGH which also > adjusts this watermark. It is probable that other users of __GFP_HIGH > should benefit from the other little bonuses that __GFP_ATOMIC gets. > > __GFP_ATOMIC also gives a warning if used with __GFP_DIRECT_RECLAIM. > There is little point to this. We already get a might_sleep() warning if > __GFP_DIRECT_RECLAIM is set. > > __GFP_ATOMIC allows the "watermark_boost" to be side-stepped. It is > probable that testing ALLOC_HARDER is a better fit here. > > __GFP_ATOMIC is used by tegra-smmu.c to check if the allocation might > sleep. This should test __GFP_DIRECT_RECLAIM instead. > > This patch: > - removes __GFP_ATOMIC > - allows __GFP_HIGH allocations to ignore watermark boosting as well > as GFP_ATOMIC requests. > - makes other adjustments as suggested by the above. > > The net result is not change to GFP_ATOMIC allocations. Other > allocations that use __GFP_HIGH will benefit from a few different extra > privileges. This affects: > xen, dm, md, ntfs3 > the vermillion frame buffer > hibernation > ksm > swap > all of which likely produce more benefit than cost if these selected > allocation are more likely to succeed quickly. > > [mgorman: Minor adjustments to rework on top of a series] > Link: https://lkml.kernel.org/r/163712397076.13692.4727608274002939094@xxxxxxxxxxxxxxxxxxxxx > Signed-off-by: NeilBrown <neilb@xxxxxxx> > Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> Acked-by: Vlastimil Babka <vbabka@xxxxxxx> Just a nit below. > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -4081,13 +4081,14 @@ static inline bool zone_watermark_fast(struct zone *z, unsigned int order, > if (__zone_watermark_ok(z, order, mark, highest_zoneidx, alloc_flags, > free_pages)) > return true; > + > /* > - * Ignore watermark boosting for GFP_ATOMIC order-0 allocations > + * Ignore watermark boosting for GFP_HIGH order-0 allocations There's no GFP_HIGH. We could either keep GFP_ATOMIC here if we want to talk about the high-level flag combo, or __GFP_HIGH if about the low-level detail. We're deep in the page allocator implementation so the latter would be OK. > * when checking the min watermark. The min watermark is the > * point where boosting is ignored so that kswapd is woken up > * when below the low watermark. > */ > - if (unlikely(!order && (gfp_mask & __GFP_ATOMIC) && z->watermark_boost > + if (unlikely(!order && (alloc_flags & ALLOC_MIN_RESERVE) && z->watermark_boost
