On 6/11/20 2:09 PM, Charan Teja Kalla wrote: > When boosting is enabled, it is observed that rate of atomic order-0 > allocation failures are high due to the fact that free levels in the > system are checked with ->watermark_boost offset. This is not a problem > for sleepable allocations but for atomic allocations which looks like > regression. > > This problem is seen frequently on system setup of Android kernel > running on Snapdragon hardware with 4GB RAM size. When no extfrag event > occurred in the system, ->watermark_boost factor is zero, thus the > watermark configurations in the system are: > _watermark = ( > [WMARK_MIN] = 1272, --> ~5MB > [WMARK_LOW] = 9067, --> ~36MB > [WMARK_HIGH] = 9385), --> ~38MB > watermark_boost = 0 > > After launching some memory hungry applications in Android which can > cause extfrag events in the system to an extent that ->watermark_boost > can be set to max i.e. default boost factor makes it to 150% of high > watermark. > _watermark = ( > [WMARK_MIN] = 1272, --> ~5MB > [WMARK_LOW] = 9067, --> ~36MB > [WMARK_HIGH] = 9385), --> ~38MB > watermark_boost = 14077, -->~57MB > > With default system configuration, for an atomic order-0 allocation to > succeed, having free memory of ~2MB will suffice. But boosting makes > the min_wmark to ~61MB thus for an atomic order-0 allocation to be > successful system should have minimum of ~23MB of free memory(from > calculations of zone_watermark_ok(), min = 3/4(min/2)). But failures are > observed despite system is having ~20MB of free memory. In the testing, > this is reproducible as early as first 300secs since boot and with > furtherlowram configurations(<2GB) it is observed as early as first > 150secs since boot. > > These failures can be avoided by excluding the ->watermark_boost in > watermark caluculations for atomic order-0 allocations. > > Fix-suggested-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> > Signed-off-by: Charan Teja Reddy <charante@xxxxxxxxxxxxxx> For the patch+fix: Acked-by: Vlastimil Babka <vbabka@xxxxxxx> The boost and highatomic stuff certainly made the whole thing more subtle. > --- > > Change in linux-next: https://lore.kernel.org/patchwork/patch/1244272/ > > mm/page_alloc.c | 36 ++++++++++++++++++++---------------- > 1 file changed, 20 insertions(+), 16 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 0c435b2..18f407e 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -3580,7 +3580,7 @@ bool zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark, > > static inline bool zone_watermark_fast(struct zone *z, unsigned int order, > unsigned long mark, int highest_zoneidx, > - unsigned int alloc_flags) > + unsigned int alloc_flags, gfp_t gfp_mask) > { > long free_pages = zone_page_state(z, NR_FREE_PAGES); > long cma_pages = 0; > @@ -3602,8 +3602,23 @@ static inline bool zone_watermark_fast(struct zone *z, unsigned int order, > mark + z->lowmem_reserve[highest_zoneidx]) > return true; > > - return __zone_watermark_ok(z, order, mark, highest_zoneidx, alloc_flags, > - free_pages); > + if (__zone_watermark_ok(z, order, mark, highest_zoneidx, alloc_flags, > + free_pages)) > + return true; > + /* > + * Ignore watermark boosting for GFP_ATOMIC order-0 allocations > + * 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 > + && ((alloc_flags & ALLOC_WMARK_MASK) == WMARK_MIN))) { > + mark = z->_watermark[WMARK_MIN]; > + return __zone_watermark_ok(z, order, mark, highest_zoneidx, > + alloc_flags, free_pages); > + } > + > + return false; > } > > bool zone_watermark_ok_safe(struct zone *z, unsigned int order, > @@ -3746,20 +3761,9 @@ static bool zone_allows_reclaim(struct zone *local_zone, struct zone *zone) > } > > mark = wmark_pages(zone, alloc_flags & ALLOC_WMARK_MASK); > - /* > - * Allow GFP_ATOMIC order-0 allocations to exclude the > - * zone->watermark_boost in their watermark calculations. > - * We rely on the ALLOC_ flags set for GFP_ATOMIC requests in > - * gfp_to_alloc_flags() for this. Reason not to use the > - * GFP_ATOMIC directly is that we want to fall back to slow path > - * thus wake up kswapd. > - */ > - if (unlikely(!order && !(alloc_flags & ALLOC_WMARK_MASK) && > - (alloc_flags & (ALLOC_HARDER | ALLOC_HIGH)))) { > - mark = zone->_watermark[WMARK_MIN]; > - } > if (!zone_watermark_fast(zone, order, mark, > - ac->highest_zoneidx, alloc_flags)) { > + ac->highest_zoneidx, alloc_flags, > + gfp_mask)) { > int ret; > > #ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT >
