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b=VbA1UGh1nC3YLNxH36lmr0c4YOCpU6zi5divlNm5Vp7tVUEfHKWIjwqb3342Ktgu+ dLDHwCayCyjiEeOWEf+EhacAOsU2xhK4a55nMVPYy30hDWPGs3zwiT/rI+Majx8b05 XJp0xB1FwXZKAdOgSNjrg50hRj7tg2ppob0usfMC7Tz1EZecNieJgmhZQ+dMRbGLv6 WAivW2gaszIZrtJTOv5XhfsX8KCmEVEXErinhfqGp4fZQjXCbd8vB8UDOTXk+jkd5Y JmeA4Av2AJiPd9enh172qDGMN7I343+BAUoJrCM0U2ifoLh3z+eZxAg4sqt7OFV7zX bxfNH3+Cosa7g== From: SeongJae Park To: Quanmin Yan Cc: SeongJae Park , akpm@linux-foundation.org, damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org, wangkefeng.wang@huawei.com, zuoze1@huawei.com, Andrew Paniakin Subject: Re: [RFC PATCH mm-next v2 12/12] mm/damon/core: prevent unnecessary overflow in damos_set_effective_quota() Date: Wed, 20 Aug 2025 15:16:33 -0700 Message-Id: <20250820221633.87243-1-sj@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250820080623.3799131-13-yanquanmin1@huawei.com> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: rpf5e7tkqp7a8kks8zh5h6fadoem4bob X-Rspam-User: X-Rspamd-Queue-Id: B12AD18000D X-Rspamd-Server: rspam01 X-HE-Tag: 1755728198-206104 X-HE-Meta: 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 Qus9tqFB xcfF3uMaSfb4q2cyt3OeO28Iyhv5yym8b9j4EebWTs3OuH9NHpLBSOMqwb1AR26+8j+EWRKhg8z+22XF3jZblr2ddKUDInbbojcPLpeUov9aewUewTNcbGZSlEE57aoiIucnQd5/LwXfk2fSt2GumBKDzD05uFnLixI565cXgsep018yvO+6xicE/wFPO4p+t0tIC3geSkRLN8/GQhKfpEzadrpMwmj9UR6TNWGyZrU/olZTrWgIohrRp2vBdfWc5GR7PoWQqBSSL4GgiydLRKTwDLfSwjoQGtkI3 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: List-Subscribe: List-Unsubscribe: + Andrew On Wed, 20 Aug 2025 16:06:22 +0800 Quanmin Yan wrote: > On 32-bit systems, the throughput calculation in function > damos_set_effective_quota() is prone to unnecessary > multiplication overflow. Using mult_frac() to fix it. Andrew Paniakin also recently found and privately reported this issue, on 64 bit systems. This can also happen on 64-bit systems, once the charged size exceeds ~17 TiB. On systems running for long time in production, this issue can actually happen. More specifically, when a DAMOS scheme having the time quota runs for long time, throughput calculation can overflow and set esz too small. As a result, speed of the scheme get unexpectedly slow. Quanmin, could you please add the above paragraph on the commit message? Also, I think this fix deserves Cc: stable@ and has no reason to be a part of this patch series. Could you please add appripriate tags like below and post again separately? Fixes: 1cd243030059 ("mm/damon/schemes: implement time quota") Reported-by: Andrew Paniakin Closes: N/A # privately reported Cc: # 5.16.x > > Signed-off-by: Quanmin Yan > --- > mm/damon/core.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/mm/damon/core.c b/mm/damon/core.c > index 980e271e42e9..38b5f842ef30 100644 > --- a/mm/damon/core.c > +++ b/mm/damon/core.c > @@ -2102,8 +2102,8 @@ static void damos_set_effective_quota(struct damos_quota *quota) > > if (quota->ms) { > if (quota->total_charged_ns) > - throughput = quota->total_charged_sz * 1000000 / > - quota->total_charged_ns; > + throughput = mult_frac(quota->total_charged_sz, 1000000, > + quota->total_charged_ns); > else > throughput = PAGE_SIZE * 1024; > esz = min(throughput * quota->ms, esz); > -- > 2.43.0 Thanks, SJ