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Thu, 4 Feb 2021 00:45:05 +0000 Subject: Re: [PATCH 2/4] hugetlg: Break earlier in add_reservation_in_range() when we can To: Peter Xu , linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: Wei Zhang , Matthew Wilcox , Linus Torvalds , Jason Gunthorpe , Gal Pressman , Christoph Hellwig , Andrea Arcangeli , Jan Kara , Kirill Shutemov , David Gibson , Mike Rapoport , Kirill Tkhai , Jann Horn , Andrew Morton References: <20210203210832.113685-1-peterx@redhat.com> <20210203210832.113685-3-peterx@redhat.com> From: Mike Kravetz Message-ID: Date: Wed, 3 Feb 2021 16:45:03 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 In-Reply-To: <20210203210832.113685-3-peterx@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [50.38.35.18] X-ClientProxiedBy: CO2PR04CA0105.namprd04.prod.outlook.com (2603:10b6:104:6::31) To MWHPR10MB1389.namprd10.prod.outlook.com (2603:10b6:300:21::22) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [192.168.2.112] (50.38.35.18) by CO2PR04CA0105.namprd04.prod.outlook.com (2603:10b6:104:6::31) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3825.19 via Frontend Transport; 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identity=mailfrom; envelope-from=""; helo=aserp2130.oracle.com; client-ip=141.146.126.79 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1612399661-223835 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 2/3/21 1:08 PM, Peter Xu wrote: > All the regions maintained in hugetlb reserved map is inclusive on "from" but > exclusive on "to". We can break earlier even if rg->from==t because it already > means no possible intersection. > > This does not need a Fixes in all cases because when it happens (rg->from==t) > we'll not break out of the loop while we should, however the next thing we'd do > is still add the last file_region we'd need and quit the loop in the next > round. So this change is not a bugfix (since the old code should still run > okay iiuc), but we'd better still touch it up to make it logically sane. > > Signed-off-by: Peter Xu > --- > mm/hugetlb.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index d2859c2aecc9..9e6ea96bf33b 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -377,7 +377,7 @@ static long add_reservation_in_range(struct resv_map *resv, long f, long t, > /* When we find a region that starts beyond our range, we've > * finished. > */ > - if (rg->from > t) > + if (rg->from >= t) > break; > > /* Add an entry for last_accounted_offset -> rg->from, and > Changing any of this code makes me nervous. However, I agree with your analysis. The change makes the code match the comment WRT the [from, to) nature of regions. Reviewed-by: Mike Kravetz -- Mike Kravetz