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dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: aws-us-west-2-caf-mail-1.web.codeaurora.org; spf=fail smtp.mailfrom=charante@codeaurora.org Subject: Re: [PATCH] mm/compaction: return proper state in should_proactive_compact_node To: Vlastimil Babka , akpm@linux-foundation.org, mhocko@suse.com, khalid.aziz@oracle.com, ngupta@nitingupta.dev, vinmenon@codeaurora.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1610546586-18998-1-git-send-email-charante@codeaurora.org> From: Charan Teja Kalla Message-ID: Date: Fri, 15 Jan 2021 20:51:18 +0530 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit 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: Thank you Vlastimil!! On 1/15/2021 6:15 PM, Vlastimil Babka wrote: > On 1/13/21 3:03 PM, Charan Teja Reddy wrote: >> should_proactive_compact_node() returns true when sum of the >> 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 the fragmentation score of the >> zone is greater than wmark_low(=wmark_high - 10). >> >> This means that the sum of the fragmentation scores of all the zones can >> exceed the wmark_high but individual zone scores can still be less than >> the wmark_low which makes the unnecessary trigger of the proactive >> compaction only to return doing nothing. >> >> Another 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 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 >> zone scores are below wmark_low, it returns without trying the >> compaction. As a result the 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. >> >> So, run the proactive compaction on the node zones only when atleast one >> of the zones fragmentation score is greater than wmark_low. This avoids >> the unnecessary deferral and retries of the compaction. >> >> Signed-off-by: Charan Teja Reddy > > Good catch about the problem, but I wonder if the solution could be better. > > fragmentation_score_node() is a weighted average of scores of all zones, that's > why fragmentation_score_zone() adjusts the score by zone_present/node_present. > > But when considering an individual zone in __compact_finished(), we shouldn't be > using fragmentation_score_zone() with the adjustment. We are not calculating the > weighted average for the whole node there, so it doesn't make sense to do the > adjustment by size. So if it simply took extfrag_for_order(...) as the score, it > should work as expected. In your example above, the score of each zone would be > above 60. If the weighted average is above wmark_high, then individual score > (not adjusted) of at least one zone has to be above wmark_high, and the extra > check using max() is not necessary. > > So I would split fragmentation_score_zone() to e.g. fragmentation_score_zone() > and fragmentation_score_zone_weighted() and call the latter only from > fragmentation_score_node(), and not from __compact_finished(). This suggestion looks good and much cleaner. Will raise V2 in couple of days. Thanks. > > Vlastimil > >> --- >> mm/compaction.c | 27 +++++++++++++++++++++++++-- >> 1 file changed, 25 insertions(+), 2 deletions(-) >> >> diff --git a/mm/compaction.c b/mm/compaction.c >> index e5acb97..f7a772a 100644 >> --- a/mm/compaction.c >> +++ b/mm/compaction.c >> @@ -1964,6 +1964,26 @@ static unsigned int fragmentation_score_node(pg_data_t *pgdat) >> return score; >> } >> >> +/* >> + * Returns the maximum of fragmentation scores of zones in a node. This is >> + * used in taking the decission of whether to trigger the proactive compaction >> + * on the zones of this node. >> + */ >> +static unsigned int fragmentation_score_node_zones_max(pg_data_t *pgdat) >> +{ >> + int zoneid; >> + unsigned int max = 0; >> + >> + for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) { >> + struct zone *zone; >> + >> + zone = &pgdat->node_zones[zoneid]; >> + max = max_t(unsigned int, fragmentation_score_zone(zone), max); >> + } >> + >> + return max; >> +} >> + >> static unsigned int fragmentation_score_wmark(pg_data_t *pgdat, bool low) >> { >> unsigned int wmark_low; >> @@ -1979,13 +1999,16 @@ static unsigned int fragmentation_score_wmark(pg_data_t *pgdat, bool low) >> >> static bool should_proactive_compact_node(pg_data_t *pgdat) >> { >> - int wmark_high; >> + int wmark_low, wmark_high; >> >> if (!sysctl_compaction_proactiveness || kswapd_is_running(pgdat)) >> return false; >> >> wmark_high = fragmentation_score_wmark(pgdat, false); >> - return fragmentation_score_node(pgdat) > wmark_high; >> + wmark_low = fragmentation_score_wmark(pgdat, true); >> + >> + return fragmentation_score_node(pgdat) > wmark_high && >> + fragmentation_score_node_zones_max(pgdat) > wmark_low; >> } >> >> static enum compact_result __compact_finished(struct compact_control *cc) >> > -- The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project