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Tue, 11 Aug 2020 01:51:52 +0000 (UTC) Received: from localhost (ovpn-13-96.pek2.redhat.com [10.72.13.96]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 000926111F; Tue, 11 Aug 2020 01:51:51 +0000 (UTC) Date: Tue, 11 Aug 2020 09:51:48 +0800 From: Baoquan He To: Mike Kravetz Cc: Wei Yang , mhocko@kernel.org, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 10/10] mm/hugetlb: not necessary to abuse temporary page to workaround the nasty free_huge_page Message-ID: <20200811015148.GA10792@MiWiFi-R3L-srv> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <129cc03e-c6d5-24f8-2f3c-f5a3cc821e76@oracle.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Rspamd-Queue-Id: B98F318086E32 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam04 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 08/10/20 at 05:19pm, Mike Kravetz wrote: > On 8/9/20 7:17 PM, Baoquan He wrote: > > On 08/07/20 at 05:12pm, Wei Yang wrote: > >> Let's always increase surplus_huge_pages and so that free_huge_page > >> could decrease it at free time. > >> > >> Signed-off-by: Wei Yang > >> --- > >> mm/hugetlb.c | 14 ++++++-------- > >> 1 file changed, 6 insertions(+), 8 deletions(-) > >> > >> diff --git a/mm/hugetlb.c b/mm/hugetlb.c > >> index 1f2010c9dd8d..a0eb81e0e4c5 100644 > >> --- a/mm/hugetlb.c > >> +++ b/mm/hugetlb.c > >> @@ -1913,21 +1913,19 @@ static struct page *alloc_surplus_huge_page(struct hstate *h, gfp_t gfp_mask, > >> return NULL; > >> > >> spin_lock(&hugetlb_lock); > >> + > >> + h->surplus_huge_pages++; > >> + h->surplus_huge_pages_node[page_to_nid(page)]++; > >> + > >> /* > >> * 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); > > > > Hmm, the temporary page way is taken intentionally in > > commit 9980d744a0428 ("mm, hugetlb: get rid of surplus page accounting tricks"). > > From code, this is done inside hugetlb_lock holding, and the code flow > > is straightforward, should be safe. Adding Michal to CC. > > > > I remember when the temporary page code was added for page migration. > The use of temporary page here was added at about the same time. Temporary > page does have one advantage in that it will not CAUSE surplus count to > exceed overcommit. This patch could cause surplus to exceed overcommit > for a very short period of time. However, do note that for this to happen > the code needs to race with a pool resize which itself could cause surplus > to exceed overcommit. > > IMO both approaches are valid. > - Advantage of temporary page is that it can not cause surplus to exceed > overcommit. Disadvantage is as mentioned in the comment 'abuse of temporary > page'. > - Advantage of this patch is that it uses existing counters. Disadvantage > is that it can momentarily cause surplus to exceed overcommit. Yeah, since it's all done inside hugetlb_lock, should be OK even though it may cause surplus to exceed overcommit. > > Unless someone has a strong opinion, I prefer the changes in this patch. Agree, I also prefer the code change in this patch, to remove the unnecessary confusion about the temporary page.