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c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc:content-transfer-encoding; bh=v2cUY6dn/8hM5Fe6/vgpIOBYGaKKOrNbvFVWUTgCzZQ=; b=rmAX02Dg7LZ0IbDb0MQtr/5CfPD+/IRvFA46yBpmePsYMnV9WMr6KUkPo1d7DX16tn RteiRb1qiLl345CshpeHED81/QPO6LjtCX8eupodh48u9vGX2sq9IwDJmwaDYoNJy5kS wsaESUjf9nBMkNYeDkeeYEZ3IZRxU6lz83RRghrisdkOETixBRAMXBp0FUc5T5BOp6k8 H9qrYl/kZwi7aQunCrjmawQg+UO5x00IOl9gDApwEWq7SFy5qy4dsRsj+pxWLUjnpvQB IeFMms4m3S8JKCTanJX7zjuT4ROh7lstE1xTVy87Hz9jn2zmCcc1BzH0JWs4uounL9MA phUw== X-Gm-Message-State: AOAM533aqlMgK20eeDROvkAFLblg76UQy4sChNIGWDyszSOo2ZlY/sWD jZkGMhEEF5IAvF+3i1tXS5jdn4OqUmS44H1zeCc= X-Google-Smtp-Source: ABdhPJy06spvE0O/+QHN1s639aC0ijZEMrz9WuEYm1H8fxF5KAdsz+aO5ojKo1uKVsFR2ceSNLKEWZswC0rNB1kK1sI= X-Received: by 2002:ae9:e20c:: with SMTP id c12mr12959301qkc.187.1593412927403; Sun, 28 Jun 2020 23:42:07 -0700 (PDT) MIME-Version: 1.0 References: <1592892828-1934-1-git-send-email-iamjoonsoo.kim@lge.com> <1592892828-1934-6-git-send-email-iamjoonsoo.kim@lge.com> <20200625120550.GF1320@dhcp22.suse.cz> <20200626073342.GU1320@dhcp22.suse.cz> In-Reply-To: <20200626073342.GU1320@dhcp22.suse.cz> From: Joonsoo Kim Date: Mon, 29 Jun 2020 15:41:37 +0900 Message-ID: Subject: Re: [PATCH v3 5/8] mm/migrate: make a standard migration target allocation function To: Michal Hocko Cc: Andrew Morton , Linux Memory Management List , LKML , kernel-team@lge.com, Vlastimil Babka , Christoph Hellwig , Roman Gushchin , Mike Kravetz , Naoya Horiguchi , Joonsoo Kim Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 73BFD1A4A0 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam04 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: 2020=EB=85=84 6=EC=9B=94 26=EC=9D=BC (=EA=B8=88) =EC=98=A4=ED=9B=84 4:33, M= ichal Hocko =EB=8B=98=EC=9D=B4 =EC=9E=91=EC=84=B1: > > On Fri 26-06-20 14:02:49, Joonsoo Kim wrote: > > 2020=EB=85=84 6=EC=9B=94 25=EC=9D=BC (=EB=AA=A9) =EC=98=A4=ED=9B=84 9:0= 5, Michal Hocko =EB=8B=98=EC=9D=B4 =EC=9E=91=EC=84=B1: > > > > > > On Tue 23-06-20 15:13:45, Joonsoo Kim wrote: > [...] > > > > -struct page *new_page_nodemask(struct page *page, > > > > - int preferred_nid, nodemask_t *nodema= sk) > > > > +struct page *alloc_migration_target(struct page *page, unsigned lo= ng private) > > > > { > > > > - gfp_t gfp_mask =3D GFP_USER | __GFP_MOVABLE | __GFP_RETRY_MAY= FAIL; > > > > + struct migration_target_control *mtc; > > > > + gfp_t gfp_mask; > > > > unsigned int order =3D 0; > > > > struct page *new_page =3D NULL; > > > > + int zidx; > > > > + > > > > + mtc =3D (struct migration_target_control *)private; > > > > + gfp_mask =3D mtc->gfp_mask; > > > > > > > > if (PageHuge(page)) { > > > > return alloc_huge_page_nodemask( > > > > - page_hstate(compound_head(page)), > > > > - preferred_nid, nodemask, 0, false); > > > > + page_hstate(compound_head(page)), mtc= ->nid, > > > > + mtc->nmask, gfp_mask, false); > > > > } > > > > > > > > if (PageTransHuge(page)) { > > > > + gfp_mask &=3D ~__GFP_RECLAIM; > > > > > > What's up with this gfp_mask modification? > > > > THP page allocation uses a standard gfp masks, GFP_TRANSHUGE_LIGHT and > > GFP_TRANHUGE. __GFP_RECLAIM flags is a big part of this standard mask d= esign. > > So, I clear it here so as not to disrupt the THP gfp mask. > > Why this wasn't really needed before? I guess I must be missing > something here. This patch should be mostly mechanical convergence of > existing migration callbacks but this change adds a new behavior AFAICS. Before this patch, a user cannot specify a gfp_mask and THP allocation uses GFP_TRANSHUGE statically. After this patch, a user can specify a gfp_mask and it could conflict with GFP_TRANSHUGE. This code tries to avoid this conflict. > It would effectively drop __GFP_RETRY_MAYFAIL and __GFP_KSWAPD_RECLAIM __GFP_RETRY_MAYFAIL isn't dropped. __GFP_RECLAIM is "___GFP_DIRECT_RECLAIM|___GFP_KSWAPD_RECLAIM". So, __GFP_KSWAPD_RECLAIM would be dropped for THP allocation. IIUC, THP allocation doesn't use __GFP_KSWAPD_RECLAIM since it's overhead i= s too large and this overhead should be given to the caller rather than system thread (kswapd) and so on. Thanks.