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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id zh15-20020a0568716b8f00b00140d421445bsm245162oab.11.2023.02.08.21.09.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 08 Feb 2023 21:09:11 -0800 (PST) Date: Wed, 8 Feb 2023 21:09:04 -0800 (PST) From: Hugh Dickins X-X-Sender: hugh@ripple.attlocal.net To: Andrew Morton cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hugh Dickins , Yang Shi , Zach O'Keefe Subject: Re: [PATCH 1/2] mm/MADV_COLLAPSE: set EAGAIN on unexpected page refcount In-Reply-To: <20230125015738.912924-1-zokeefe@google.com> Message-ID: References: <20230125015738.912924-1-zokeefe@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 66D5A40009 X-Rspam-User: X-Stat-Signature: hgoctdmatz5gjzpkn4zsw5gofar43k9y X-HE-Tag: 1675919353-722760 X-HE-Meta: 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 KHg8QUX9 iN+IZzIjVl2vyVXaJR+OZjal9dCpRl83R/4cd5oTai87YTQ9UtibJldx11+pjJJTgeIAQyOh9/IX+2k2Y0bK/PjunXGMoJ8UholuithUHqh8UgO7qU6GraaXw26j8Q5zv/U4VolJMKmgydJGD14+t3WPKtLpxfa5kj3dKIbKn/ZRanqtos1ofcSByg6SIMb5DQRVQNYzS97/5jH553u2Qf6nsO1a0vy4U3wHhy6DExN2bxLnnL0b3GHT9vdTu7XVQqJACG1AzZHbmCVqhKILByDuM6ip7zuoIDSJEIaLAiSdXMdN5x9f4ni63td9qS6G8LTbNa/SW9x/cpQ4D9fuPveIa1CORUWyBVsTYJKrUxciiO+tYaXZivVLK46wXRFP6jFVXHg5Q7YeyMqYfyb3SxhnxflhFaytSYA1J8lJecqT62w2H/cz3oBtQZ4+u51IhsXnOq4udr0G6ttkzJmiQ32mT7g== 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 Tue, 24 Jan 2023, Zach O'Keefe wrote: > During collapse, in a few places we check to see if a given small page > has any unaccounted references. If the refcount on the page doesn't > match our expectations, it must be there is an unknown user concurrently > interested in the page, and so it's not safe to move the contents > elsewhere. However, the unaccounted pins are likely an ephemeral state. > > In such a situation, make MADV_COLLAPSE set EAGAIN errno, indicating that > collapse may succeed on retry. > > Fixes: 7d8faaf15545 ("mm/madvise: introduce MADV_COLLAPSE sync hugepage collapse") > Reported-by: Hugh Dickins > Signed-off-by: Zach O'Keefe This was Reviewed-by: Yang Shi and now I'll give it a nudge with Acked-by: Hugh Dickins since it hasn't appeared in mm-unstable or linux-next yet: I think its Cc:stable sibling 2/2, already in 6.2-rc, got all the attention. Thanks! Hugh > > --- > mm/khugepaged.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index e23619bfecc4..fa38cae240b9 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -2712,6 +2712,7 @@ static int madvise_collapse_errno(enum scan_result r) > case SCAN_CGROUP_CHARGE_FAIL: > return -EBUSY; > /* Resource temporary unavailable - trying again might succeed */ > + case SCAN_PAGE_COUNT: > case SCAN_PAGE_LOCK: > case SCAN_PAGE_LRU: > case SCAN_DEL_PAGE_LRU: > -- > 2.39.1.405.gd4c25cc71f-goog