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[209.132.183.28]) by mx.google.com with ESMTPS id w50si11741729qta.271.2019.08.09.09.35.55 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 09 Aug 2019 09:35:55 -0700 (PDT) Received-SPF: pass (google.com: domain of oleg@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of oleg@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=oleg@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id BEBED300BEAC; Fri, 9 Aug 2019 16:35:54 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.136]) by smtp.corp.redhat.com (Postfix) with SMTP id 00E1B19C70; Fri, 9 Aug 2019 16:35:52 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Fri, 9 Aug 2019 18:35:54 +0200 (CEST) Date: Fri, 9 Aug 2019 18:35:52 +0200 From: Oleg Nesterov To: Song Liu Cc: Linux Kernel Mailing List , Linux MM , "akpm@linux-foundation.org" , "matthew.wilcox@oracle.com" , "kirill.shutemov@linux.intel.com" , Kernel Team , "william.kucharski@oracle.com" , "srikar@linux.vnet.ibm.com" Subject: Re: [PATCH v12 3/6] mm, thp: introduce FOLL_SPLIT_PMD Message-ID: <20190809163551.GB21489@redhat.com> References: <20190807233729.3899352-1-songliubraving@fb.com> <20190807233729.3899352-4-songliubraving@fb.com> <20190808163745.GC7934@redhat.com> <48316E06-10B2-439C-AD10-3EC8C86C259C@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <48316E06-10B2-439C-AD10-3EC8C86C259C@fb.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.42]); Fri, 09 Aug 2019 16:35:54 +0000 (UTC) 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 08/08, Song Liu wrote: > > > On Aug 8, 2019, at 9:37 AM, Oleg Nesterov wrote: > > > > On 08/07, Song Liu wrote: > >> > >> @@ -399,7 +399,7 @@ static struct page *follow_pmd_mask(struct vm_area_struct *vma, > >> spin_unlock(ptl); > >> return follow_page_pte(vma, address, pmd, flags, &ctx->pgmap); > >> } > >> - if (flags & FOLL_SPLIT) { > >> + if (flags & (FOLL_SPLIT | FOLL_SPLIT_PMD)) { > >> int ret; > >> page = pmd_page(*pmd); > >> if (is_huge_zero_page(page)) { > >> @@ -408,7 +408,7 @@ static struct page *follow_pmd_mask(struct vm_area_struct *vma, > >> split_huge_pmd(vma, pmd, address); > >> if (pmd_trans_unstable(pmd)) > >> ret = -EBUSY; > >> - } else { > >> + } else if (flags & FOLL_SPLIT) { > >> if (unlikely(!try_get_page(page))) { > >> spin_unlock(ptl); > >> return ERR_PTR(-ENOMEM); > >> @@ -420,6 +420,10 @@ static struct page *follow_pmd_mask(struct vm_area_struct *vma, > >> put_page(page); > >> if (pmd_none(*pmd)) > >> return no_page_table(vma, flags); > >> + } else { /* flags & FOLL_SPLIT_PMD */ > >> + spin_unlock(ptl); > >> + split_huge_pmd(vma, pmd, address); > >> + ret = pte_alloc(mm, pmd) ? -ENOMEM : 0; > >> } > > > > Can't resist, let me repeat that I do not like this patch because imo > > it complicates this code for no reason. > > Personally, I don't think this is more complicated than your version. I do, but of course this is subjective. > Also, if some code calls follow_pmd_mask() with flags contains both > FOLL_SPLIT and FOLL_SPLIT_PMD, we should honor FOLL_SPLIT and split the > huge page. Heh. why not other way around? > Of course, there is no code that sets both flags. and of course, nobody should ever pass both FOLL_SPLIT and FOLL_SPLIT_PMD, perhaps this deserves a warning. Not to mention that it would be nice to kill FOLL_SPLIT which has a single user, but this is another story. Oleg.