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Tue, 19 Jan 2021 15:42:58 +0000 Received: from pps.filterd (aserp3020.oracle.com [127.0.0.1]) by aserp3020.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 10JFZi2F083638; Tue, 19 Jan 2021 15:42:58 GMT Received: from aserv0122.oracle.com (aserv0122.oracle.com [141.146.126.236]) by aserp3020.oracle.com with ESMTP id 3661equj83-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 19 Jan 2021 15:42:58 +0000 Received: from abhmp0005.oracle.com (abhmp0005.oracle.com [141.146.116.11]) by aserv0122.oracle.com (8.14.4/8.14.4) with ESMTP id 10JFgunt013377; Tue, 19 Jan 2021 15:42:56 GMT Received: from [10.65.183.184] (/10.65.183.184) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Tue, 19 Jan 2021 07:42:56 -0800 Subject: Re: [PATCH V3] mm/compaction: correct deferral logic for proactive compaction To: Charan Teja Reddy , akpm@linux-foundation.org, vbabka@suse.cz, mhocko@suse.com, ngupta@nitingupta.dev, vinmenon@codeaurora.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1610989938-31374-1-git-send-email-charante@codeaurora.org> From: Khalid Aziz Organization: Oracle Corp Message-ID: <5343d1b9-a9b1-9967-1f88-5d37ec93274c@oracle.com> Date: Tue, 19 Jan 2021 08:42:55 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.5.0 MIME-Version: 1.0 In-Reply-To: <1610989938-31374-1-git-send-email-charante@codeaurora.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9868 signatures=668683 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 spamscore=0 phishscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 suspectscore=0 malwarescore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2101190094 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9868 signatures=668683 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 impostorscore=0 spamscore=0 mlxlogscore=999 clxscore=1011 bulkscore=0 adultscore=0 lowpriorityscore=0 suspectscore=0 phishscore=0 mlxscore=0 malwarescore=0 priorityscore=1501 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2101190094 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 1/18/21 10:12 AM, Charan Teja Reddy wrote: > should_proactive_compact_node() returns true when sum of the > weighted fragmentation score of all the zones in the node is greater > than the wmark_high of compaction, which then triggers the proactive > compaction that operates on the individual zones of the node. But > proactive compaction runs on the zone only when its weighted > fragmentation score is greater than wmark_low(=wmark_high - 10). > > This means that the sum of the weighted fragmentation scores of all the > zones can exceed the wmark_high but individual weighted fragmentation > zone scores can still be less than wmark_low which makes the unnecessary > trigger of the proactive compaction only to return doing nothing. > > Issue with the return of proactive compaction with out even trying is > its deferral. It is simply deferred for 1 << COMPACT_MAX_DEFER_SHIFT if > the scores across the proactive compaction is same, thinking that > compaction didn't make any progress but in reality it didn't even try. > With the delay between successive retries for proactive compaction is > 500msec, it can result into the deferral for ~30sec with out even trying > the proactive compaction. > > Test scenario is that: compaction_proactiveness=50 thus the wmark_low = > 50 and wmark_high = 60. System have 2 zones(Normal and Movable) with > sizes 5GB and 6GB respectively. After opening some apps on the android, > the weighted fragmentation scores of these zones are 47 and 49 > respectively. Since the sum of these fragmentation scores are above the > wmark_high which triggers the proactive compaction and there since the > individual zones weighted fragmentation scores are below wmark_low, it > returns without trying the proactive compaction. As a result the > weighted fragmentation scores of the zones are still 47 and 49 which > makes the existing logic to defer the compaction thinking that > noprogress is made across the compaction. > > Fix this by checking just zone fragmentation score, not the weighted, in > __compact_finished() and use the zones weighted fragmentation score in > fragmentation_score_node(). In the test case above, If the weighted > average of is above wmark_high, then individual score (not adjusted) of > atleast one zone has to be above wmark_high. Thus it avoids the > unnecessary trigger and deferrals of the proactive compaction. > > Fix-suggested-by: Vlastimil Babka > Signed-off-by: Charan Teja Reddy > --- > > Changes in V3: Addressed suggestions from Vlastimil > > Changes in V2: https://lore.kernel.org/patchwork/patch/1366862/ > > Changes in V1: https://lore.kernel.org/patchwork/patch/1364646/ > > mm/compaction.c | 20 ++++++++++++++------ > 1 file changed, 14 insertions(+), 6 deletions(-) > > diff --git a/mm/compaction.c b/mm/compaction.c > index e5acb97..ccddb3a 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -1925,20 +1925,28 @@ static bool kswapd_is_running(pg_data_t *pgdat) > > /* > * A zone's fragmentation score is the external fragmentation wrt to the > - * COMPACTION_HPAGE_ORDER scaled by the zone's size. It returns a value > - * in the range [0, 100]. > + * COMPACTION_HPAGE_ORDER. It returns a value in the range [0, 100]. > + */ > +static unsigned int fragmentation_score_zone(struct zone *zone) > +{ > + return extfrag_for_order(zone, COMPACTION_HPAGE_ORDER); > +} > + > +/* > + * A weighted zone's fragmentation score is the external fragmentation > + * wrt to the COMPACTION_HPAGE_ORDER scaled by the zone's size. It > + * returns a value in the range [0, 100]. > * > * The scaling factor ensures that proactive compaction focuses on larger > * zones like ZONE_NORMAL, rather than smaller, specialized zones like > * ZONE_DMA32. For smaller zones, the score value remains close to zero, > * and thus never exceeds the high threshold for proactive compaction. > */ > -static unsigned int fragmentation_score_zone(struct zone *zone) > +static unsigned int fragmentation_score_zone_weighted(struct zone *zone) > { > unsigned long score; > > - score = zone->present_pages * > - extfrag_for_order(zone, COMPACTION_HPAGE_ORDER); > + score = zone->present_pages * fragmentation_score_zone(zone); > return div64_ul(score, zone->zone_pgdat->node_present_pages + 1); > } > > @@ -1958,7 +1966,7 @@ static unsigned int fragmentation_score_node(pg_data_t *pgdat) > struct zone *zone; > > zone = &pgdat->node_zones[zoneid]; > - score += fragmentation_score_zone(zone); > + score += fragmentation_score_zone_weighted(zone); > } > > return score; > Looks good. Reviewed-by: Khalid Aziz