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Tue, 11 Aug 2020 23:25:04 +0000 Received: from pps.filterd (userp3020.oracle.com [127.0.0.1]) by userp3020.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 07BNJZ66043088; Tue, 11 Aug 2020 23:25:04 GMT Received: from aserv0122.oracle.com (aserv0122.oracle.com [141.146.126.236]) by userp3020.oracle.com with ESMTP id 32u3h2ckbn-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 11 Aug 2020 23:25:04 +0000 Received: from abhmp0017.oracle.com (abhmp0017.oracle.com [141.146.116.23]) by aserv0122.oracle.com (8.14.4/8.14.4) with ESMTP id 07BNP2hd027654; Tue, 11 Aug 2020 23:25:03 GMT Received: from [192.168.2.112] (/50.38.35.18) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Tue, 11 Aug 2020 23:25:02 +0000 Subject: Re: [PATCH 10/10] mm/hugetlb: not necessary to abuse temporary page to workaround the nasty free_huge_page To: Wei Yang Cc: Michal Hocko , Baoquan He , akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20200807091251.12129-1-richard.weiyang@linux.alibaba.com> <20200807091251.12129-11-richard.weiyang@linux.alibaba.com> <20200810021737.GV14854@MiWiFi-R3L-srv> <129cc03e-c6d5-24f8-2f3c-f5a3cc821e76@oracle.com> <20200811015148.GA10792@MiWiFi-R3L-srv> <20200811065406.GC4793@dhcp22.suse.cz> <20200811231932.GA33666@L-31X9LVDL-1304.local> From: Mike Kravetz Message-ID: <5125772b-2939-e71f-da4a-374cb74c9061@oracle.com> Date: Tue, 11 Aug 2020 16:25:01 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20200811231932.GA33666@L-31X9LVDL-1304.local> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9710 signatures=668679 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 adultscore=0 mlxlogscore=999 mlxscore=0 malwarescore=0 spamscore=0 suspectscore=2 phishscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2008110169 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9710 signatures=668679 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 priorityscore=1501 lowpriorityscore=0 bulkscore=0 impostorscore=0 phishscore=0 clxscore=1015 spamscore=0 malwarescore=0 adultscore=0 mlxlogscore=999 mlxscore=0 suspectscore=2 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2008110169 X-Rspamd-Queue-Id: BC82228A4E8 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam05 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 8/11/20 4:19 PM, Wei Yang wrote: > On Tue, Aug 11, 2020 at 02:43:28PM -0700, Mike Kravetz wrote: >> Subject: [PATCH] hugetlb: optimize race error return in >> alloc_surplus_huge_page >> >> The routine alloc_surplus_huge_page() could race with with a pool >> size change. If this happens, the allocated page may not be needed. >> To free the page, the current code will 'Abuse temporary page to >> workaround the nasty free_huge_page codeflow'. Instead, directly >> call the low level routine that free_huge_page uses. This works >> out well because the page is new, we hold the only reference and >> already hold the hugetlb_lock. >> >> Signed-off-by: Mike Kravetz >> --- >> mm/hugetlb.c | 13 ++++++++----- >> 1 file changed, 8 insertions(+), 5 deletions(-) >> >> diff --git a/mm/hugetlb.c b/mm/hugetlb.c >> index 590111ea6975..ac89b91fba86 100644 >> --- a/mm/hugetlb.c >> +++ b/mm/hugetlb.c >> @@ -1923,14 +1923,17 @@ static struct page *alloc_surplus_huge_page(struct hstate *h, gfp_t gfp_mask, >> /* >> * We could have raced with the pool size change. >> * Double check that and simply deallocate the new page >> - * if we would end up overcommiting the surpluses. Abuse >> - * temporary page to workaround the nasty free_huge_page >> - * codeflow >> + * if we would end up overcommiting the surpluses. >> */ >> if (h->surplus_huge_pages >= h->nr_overcommit_huge_pages) { >> - SetPageHugeTemporary(page); >> + /* >> + * Since this page is new, we hold the only reference, and >> + * we already hold the hugetlb_lock call the low level free >> + * page routine. This saves at least a lock roundtrip. > > The change looks good to me, while I may not understand the "lock roundtrip". > You mean we don't need to release the hugetlb_lock? Correct. Normally we would free the page via free_huge_page() processing. To do that we need to drop hugetlb_lock and call put_page/free_huge_page which will need to acquire the hugetlb_lock again. -- Mike Kravetz > >> + */ >> + (void)put_page_testzero(page); /* don't call destructor */ >> + update_and_free_page(h, page); >> spin_unlock(&hugetlb_lock); >> - put_page(page); >> return NULL; >> } else { >> h->surplus_huge_pages++; >> -- >> 2.25.4