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Tue, 05 Jan 2021 01:33:01 +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 1051SNnP115782; Tue, 5 Jan 2021 01:33:00 GMT Received: from userv0122.oracle.com (userv0122.oracle.com [156.151.31.75]) by aserp3020.oracle.com with ESMTP id 35v1f81114-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 05 Jan 2021 01:33:00 +0000 Received: from abhmp0009.oracle.com (abhmp0009.oracle.com [141.146.116.15]) by userv0122.oracle.com (8.14.4/8.14.4) with ESMTP id 1051WtIq031261; Tue, 5 Jan 2021 01:32:57 GMT Received: from [192.168.2.112] (/50.38.35.18) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Mon, 04 Jan 2021 17:32:55 -0800 Subject: Re: [PATCH 4/6] mm: hugetlb: add return -EAGAIN for dissolve_free_huge_page To: Muchun Song , akpm@linux-foundation.org Cc: hillf.zj@alibaba-inc.com, n-horiguchi@ah.jp.nec.com, ak@linux.intel.com, yongjun_wei@trendmicro.com.cn, mhocko@suse.cz, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20210104065843.5658-1-songmuchun@bytedance.com> <20210104065843.5658-4-songmuchun@bytedance.com> From: Mike Kravetz Message-ID: Date: Mon, 4 Jan 2021 17:32:54 -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: <20210104065843.5658-4-songmuchun@bytedance.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=9854 signatures=668683 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxlogscore=999 phishscore=0 suspectscore=0 spamscore=0 bulkscore=0 adultscore=0 mlxscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2101050005 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9854 signatures=668683 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 clxscore=1015 phishscore=0 bulkscore=0 spamscore=0 impostorscore=0 suspectscore=0 adultscore=0 mlxlogscore=999 mlxscore=0 malwarescore=0 lowpriorityscore=0 priorityscore=1501 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2101050005 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 1/3/21 10:58 PM, Muchun Song wrote: > When dissolve_free_huge_page() races with __free_huge_page(), we can > do a retry. Because the race window is small. In general, I agree that the race window is small. However, worst case would be if the freeing of the page is put on a work queue. Is it acceptable to keep retrying in that case? In addition, the 'Free some vmemmap' series may slow the free_huge_page path even more. In these worst case scenarios, I am not sure we want to just spin retrying. -- Mike Kravetz > > Signed-off-by: Muchun Song > --- > mm/hugetlb.c | 16 +++++++++++----- > 1 file changed, 11 insertions(+), 5 deletions(-) > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index 72608008f8b4..db00ae375d2a 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -1763,10 +1763,11 @@ static int free_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed, > * nothing for in-use hugepages and non-hugepages. > * This function returns values like below: > * > - * -EBUSY: failed to dissolved free hugepages or the hugepage is in-use > - * (allocated or reserved.) > - * 0: successfully dissolved free hugepages or the page is not a > - * hugepage (considered as already dissolved) > + * -EAGAIN: race with __free_huge_page() and can do a retry > + * -EBUSY: failed to dissolved free hugepages or the hugepage is in-use > + * (allocated or reserved.) > + * 0: successfully dissolved free hugepages or the page is not a > + * hugepage (considered as already dissolved) > */ > int dissolve_free_huge_page(struct page *page) > { > @@ -1815,8 +1816,10 @@ int dissolve_free_huge_page(struct page *page) > * We should make sure that the page is already on the free list > * when it is dissolved. > */ > - if (unlikely(!PageHugeFreed(head))) > + if (unlikely(!PageHugeFreed(head))) { > + rc = -EAGAIN; > goto out; > + } > > /* > * Move PageHWPoison flag from head page to the raw error page, > @@ -1857,7 +1860,10 @@ int dissolve_free_huge_pages(unsigned long start_pfn, unsigned long end_pfn) > > for (pfn = start_pfn; pfn < end_pfn; pfn += 1 << minimum_order) { > page = pfn_to_page(pfn); > +retry: > rc = dissolve_free_huge_page(page); > + if (rc == -EAGAIN) > + goto retry; > if (rc) > break; > } >