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Thu, 14 Jan 2021 19:16:10 +0000 Received: from pps.filterd (aserp3020.oracle.com [127.0.0.1]) by aserp3020.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 10EJBmfX006237; Thu, 14 Jan 2021 19:16:09 GMT Received: from userv0121.oracle.com (userv0121.oracle.com [156.151.31.72]) by aserp3020.oracle.com with ESMTP id 360keaa1n3-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 14 Jan 2021 19:16:09 +0000 Received: from abhmp0007.oracle.com (abhmp0007.oracle.com [141.146.116.13]) by userv0121.oracle.com (8.14.4/8.13.8) with ESMTP id 10EJG6U0028547; Thu, 14 Jan 2021 19:16:06 GMT Received: from [192.168.2.112] (/50.38.35.18) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Thu, 14 Jan 2021 11:16:06 -0800 Subject: Re: [PATCH] mm/hugetlb: avoid unnecessary hugetlb_acct_memory() call To: Miaohe Lin , akpm@linux-foundation.org Cc: David Hildenbrand , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20210114113140.23069-1-linmiaohe@huawei.com> <853d6aa4-b84c-7ac2-00d4-402893fcf6b3@redhat.com> From: Mike Kravetz Message-ID: Date: Thu, 14 Jan 2021 11:16:05 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 MIME-Version: 1.0 In-Reply-To: <853d6aa4-b84c-7ac2-00d4-402893fcf6b3@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9864 signatures=668683 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 adultscore=0 suspectscore=0 spamscore=0 mlxlogscore=999 malwarescore=0 bulkscore=0 mlxscore=0 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2101140109 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9864 signatures=668683 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 spamscore=0 phishscore=0 impostorscore=0 bulkscore=0 adultscore=0 suspectscore=0 malwarescore=0 lowpriorityscore=0 clxscore=1015 mlxlogscore=999 mlxscore=0 priorityscore=1501 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2101140109 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 1/14/21 4:32 AM, David Hildenbrand wrote: > On 14.01.21 12:31, Miaohe Lin wrote: >> When gbl_reserve is 0, hugetlb_acct_memory() will do nothing except holding >> and releasing hugetlb_lock. > > So, what's the deal then? Adding more code? > > If this is a performance improvement, we should spell it out. Otherwise > I don't see a real benefit of this patch. > Thanks for finding/noticing this. As David points out, the commit message should state that this is a performance improvement. Mention that such a change avoids an unnecessary hugetlb_lock lock/unlock cycle. You can also mention that this unnecessary lock cycle is happening on 'most' hugetlb munmap operations. >> >> Signed-off-by: Miaohe Lin >> --- >> mm/hugetlb.c | 3 ++- >> 1 file changed, 2 insertions(+), 1 deletion(-) >> >> diff --git a/mm/hugetlb.c b/mm/hugetlb.c >> index 737b2dce19e6..fe2da9ad6233 100644 >> --- a/mm/hugetlb.c >> +++ b/mm/hugetlb.c >> @@ -5241,7 +5241,8 @@ long hugetlb_unreserve_pages(struct inode *inode, long start, long end, >> * reservations to be released may be adjusted. >> */ >> gbl_reserve = hugepage_subpool_put_pages(spool, (chg - freed)); >> - hugetlb_acct_memory(h, -gbl_reserve); >> + if (gbl_reserve) >> + hugetlb_acct_memory(h, -gbl_reserve); It is true that gbl_reserve is likely to be 0 in this code path. However, there are other code paths where hugetlb_acct_memory is called with a delta value of 0 as well. I would rather see a simple check at the beginning of hugetlb_acct_memory like. if (!delta) return 0; -- Mike Kravetz >> >> return 0; >> } >> > >