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Thu, 21 Aug 2025 09:18:44 -0700 (PDT) MIME-Version: 1.0 References: <20250821155833.57597-1-sj@kernel.org> In-Reply-To: <20250821155833.57597-1-sj@kernel.org> From: Sang-Heon Jeon Date: Fri, 22 Aug 2025 01:18:32 +0900 X-Gm-Features: Ac12FXzi3h9xpcGpuOkzdRydRGIYtRmhUHBmyrmZ9RELoX71HPL9qduVXxKXs_E Message-ID: Subject: Re: [PATCH v2] mm/damon/core: set quota->charged_from to jiffies at first charge window To: SeongJae Park Cc: honggyu.kim@sk.com, damon@lists.linux.dev, linux-mm@kvack.org, stable@vger.kernel.org, Andrew Morton Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 9A9BC160004 X-Stat-Signature: rcq3cbra5zzgucbhknhbttsj4fxs75rr X-Rspam-User: X-HE-Tag: 1755793125-390111 X-HE-Meta: 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 RmkJdRQ/ hIUR6QYfDmh7JpXDWaxpWXiQCBIAJYsy1Qof2kH5TEaV6YqtjAVzDw7GQWJntiZAe8Pk0PQP69KHmw8iCHNzQCxOnKLJDzeS7El94TGTN7pVRrYAAulRaLPtCCZnadwAAGSmU9arpNAGXYlkdM6zkIy/x/BjDfbMn92UaMqUfaPMA1Z86P1H8qliWiCaro9+oy/9xziQWVle8tfNBJwBrNa4LGYyTaKtZDr7hsBmzzEWf983tF00jfywJHK3G+15wUaZuCFWPdYvYPOy38ZbBsnmNmGAwK8pmR6NeNKt+9bLUhRoRyZje98o+l0Ba9wuqSupX88phucQ23WX0ApqMThLyVUfN8ULP/3tEdvwTmz2cS0LRM/oipp2vQvmK3E0E67ZEnSu6EsFwDLd02h3WFk5lsNpkXhZ5fSGSqkeLhL5cCkSwcmKXcinjrsORZ8nKPc+u 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: On Fri, Aug 22, 2025 at 12:58=E2=80=AFAM SeongJae Park wrot= e: > > On Thu, 21 Aug 2025 20:06:58 +0900 Sang-Heon Jeon = wrote: > > > On Thu, Aug 21, 2025 at 2:41=E2=80=AFPM SeongJae Park w= rote: > [...] > > > Let's restart. Could you please rewrite the commit log for this patc= h and send > > > the draft as a reply to this? > > > > > > We can further discuss on the new draft if it has more things to impr= ove. And > > > once the discussion is finalized, you can post v4 of this patch with = the > > > updated commit message. > > > > Good Idea. This is the draft for commit message. Also, Thank you for > > your patience and understanding. > > Thank you for accepting my humble suggestion. > > > > > Kernel initialize "jiffies" timer as 5 minutes below zero, as shown in > > include/linux/jiffies.h > > > > /* > > * Have the 32 bit jiffies value wrap 5 minutes after boot > > * so jiffies wrap bugs show up earlier. > > */ > > #define INITIAL_JIFFIES ((unsigned long)(unsigned int) (-300*HZ)) > > > > And jiffies comparison help functions cast unsigned value to signed to > > cover wraparound > > > > #define time_after_eq(a,b) \ > > (typecheck(unsigned long, a) && \ > > typecheck(unsigned long, b) && \ > > ((long)((a) - (b)) >=3D 0)) > > > > When quota->charged_from is initialized to 0, time_after_eq() can incor= rectly > > return FALSE even after reset_interval has elapsed. This occurs when > > (jiffies - reset_interval) produces a value with MSB=3D1, which is inte= rpreted > > as negative in signed arithmetic. > > > > This issue primarily affects 32-bit systems because: > > On 64-bit systems: MSB=3D1 values occur after ~292 million years from b= oot > > (assuming HZ=3D1000), almost impossible. > > > > On 32-bit systems: MSB=3D1 values occur during the first 5 minutes afte= r boot, > > and the second half of every jiffies wraparound cycle, starting from da= y 25 > > (assuming HZ=3D1000) > > > > When above unexpected FALSE return from time_after_eq() occurs, the > > charging window will not reset. The user impact depends on esz value > > at that time. > > > > If esz is 0, scheme ignores configured quotas and runs without any > > limits. > > > > If esz is not 0, scheme stops working once the quota is exhausted. It > > remains until the charging window finally resets. > > > > So, change quota->charged_from to jiffies at damos_adjust_quota() when > > it is considered as the first charge window. By this change, we can avo= id > > unexpected FALSE return from time_after_eq() > > This new draft looks good to me. I find nothing to further modify. Coul= d you > please send v3 of this patch with the above commit log? I'm really glad to hear that! Your thoughtful comments really brought this together. > > Thanks, > SJ > > [...] Best Regards Sang-Heon Jeon