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a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=KonOja3gt2Do8uQ+N5ZsHzrJgX0wr3tVjawKXZm29t0=; b=ycn6Hh84JM54VGkYuU4FH0h+1Ri0PRrQ9/qMmOe9IKwLMUdid3mFbpAGftUaVCBWd0 xdEf+PqUy9UXdmFgrUMWJYNerPY4mYpcOQbdlIByMBExkuLqZCe4Qvr3+XlsamAN2BSJ isAwszomKb8M5YIBReoAp21RMs9aBtXajzh90yFiepxJUaSOJHDF09sKsdtDWY5Lduy6 fzoSD3bRm6YRPd9Km3Q3Qi6M1qsksG5uBA+nUfFlwQQymW+mcYegfDLSUzrBaIscWaTa zReLxZMSwAkUNtG/0x+/nDNeC3vpyYH9Mqlyf429ajhP34kTeiOU3OHborjuxcezC4F6 a80Q== X-Gm-Message-State: AFqh2kp1xbYoWMz1BsIK/pCf3dnqM25i67fgVpw4NSD8KWm/+lElpBSU RmWpygiydQBcV7uvmEfVub08lotlda0VmY/0opY1Hg== X-Google-Smtp-Source: AMrXdXuE+Jz47ACBTQhXSDrEl9W9Z4cli3e6SXSyl0QMgoIf6o2paDsXXUoCTlyv4rQ8nnF9koQftCuvIKwPkpdFMDY= X-Received: by 2002:a05:6000:1367:b0:28c:295f:3369 with SMTP id q7-20020a056000136700b0028c295f3369mr748046wrz.355.1672860851698; Wed, 04 Jan 2023 11:34:11 -0800 (PST) MIME-Version: 1.0 References: <20230101230042.244286-1-jthoughton@google.com> In-Reply-To: From: James Houghton Date: Wed, 4 Jan 2023 19:34:00 +0000 Message-ID: Subject: Re: [PATCH] hugetlb: unshare some PMDs when splitting VMAs To: Peter Xu Cc: Mike Kravetz , Muchun Song , Axel Rasmussen , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" X-Stat-Signature: uc3kzzupjrwad48d1izwp4yy5e8dorfz X-Rspam-User: X-Rspamd-Queue-Id: 117244000A X-Rspamd-Server: rspam06 X-HE-Tag: 1672860852-146791 X-HE-Meta: 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 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: > > @@ -4828,6 +4830,23 @@ static int hugetlb_vm_op_split(struct vm_area_struct *vma, unsigned long addr) > > { > > if (addr & ~(huge_page_mask(hstate_vma(vma)))) > > return -EINVAL; > > + > > + /* We require PUD_SIZE VMA alignment for PMD sharing. */ > > I can get the point, but it reads slightly awkward. How about: > > /* > * If the address to split can be in the middle of a shared pmd > * range, unshare before split the vma. > */ > How about: /* * PMD sharing is only possible for PUD_SIZE-aligned address ranges * in HugeTLB VMAs. If we will lose PUD_SIZE alignment due to this split, * unshare PMDs in the PUD_SIZE interval surrounding addr now. */ > I remember you had a helper to check pmd sharing possibility. Can use here > depending on whether that existed in the code base or in your hgm series > (or just pick that up with this one?). Right, it introduces `pmd_sharing_possible` but I don't think it helps here. > > > + if (addr & ~PUD_MASK) { > > + /* > > + * hugetlb_vm_op_split is called right before we attempt to > > + * split the VMA. We will need to unshare PMDs in the old and > > + * new VMAs, so let's unshare before we split. > > + */ > > + unsigned long floor = addr & PUD_MASK; > > + unsigned long ceil = floor + PUD_SIZE; > > + > > + if (floor < vma->vm_start || ceil >= vma->vm_end) > > s/>=/>/? Indeed, thanks. > > > + /* PMD sharing is already impossible. */ > > + return 0; > > IMHO slightly cleaner to write in the reversed way and let it fall through: > > if (floor >= vma->vm_start && ceil <= vma->vm_end) > hugetlb_unshare_pmds(vma, floor, ceil); Will do. > > Thanks, > Thanks Peter!