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b=ma3mjiH61nNEDh7izYui/7QrjOoglBmcXne6eWRWUIOBZbe9IXEBoxr5zSTBqD38/ cVcljtJIDfSNx6eWcpo4cEr+GQZWgC/F4nvDySDRmO74Cy/aNG2JSQqgBGPkO91vEC bkpaVZ79YQMRunRGZn67AN2xLyVdrg3YT77DcCn7G4gecRK6rMbGl3mFF2K1Nl3T5P jPAwbKOf1tx8Pz2/HOlhirMDv1ZU2sbMv3ZVD4c2w9c7+V44BioJ/r4bALZ+1CT9zt DM6Lo9X15WqpBJX4jNWXva4efUd62euN7TiAhsgeXXFJb7dg8OG3vq2h17fXvcNfb7 c67rM4czVINnw== From: SeongJae Park To: Liew Rui Yan Cc: SeongJae Park , damon@lists.linux.dev, linux-mm@kvack.org Subject: Re: [PATCH] mm/damon: validate addr_unit to be power of 2 Date: Fri, 27 Mar 2026 07:14:49 -0700 Message-ID: <20260327141450.4345-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260327062627.66426-1-aethernet65535@gmail.com> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: AE9D64000C X-Stat-Signature: enfgcs8qxqmhuogbbs8z68ddt5x8pwuf X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1774620893-804342 X-HE-Meta: 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 6SE0gz1T Nd0Tkr7cONpIbErdI6EbfNlr1eVQtDhQMxPL3GxlAd0K7aFkPinIjlGG+gXQFshdfz+f6wdtpUY4VtdHx+5+s9bfmRAx8BQnkWLDZjXyIinVTqevKLHV0w0kgrTZVn0upXvyJfD9gcFvBuLmcSvxmg1DHVRg/p6UZ5LgXdv5diQG0LICKZBuxzpsl69TcQwYYvsymjjkJsLBL/nF1nzexrW8lu1Udv22i3nPJoUaqhHBjoOW1pqtaWSgUp/U5XxUK5IKWYB6qVUIEJc5kR/mL7CwDPQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Liew, Unfortunately I'm bit confused about this patch. Please answer below questions. On Fri, 27 Mar 2026 14:26:27 +0800 Liew Rui Yan wrote: > Problem > ======= > The 'addr_unit' must be a power of 2 for correct address alignment > calculations. It is required to be a power of 2 only if it is smaller than PAGE_SIZE. Refer to commit d8fe5d2a3379 ("Docs/mm/damon/design: document the power-of-two limitation for addr_unit") for more details. > Previously, Can we make the timing more explicitly? I'm confusing when is the time you are mentioning, since a behavioral change was made recently, by commit c80f46ac228b ("mm/damon/core: disallow non-power of two min_region_sz"). > writing a non-power-of-2 value > (e.g., addr_unit=3) would be accepted by the sysfs store callback, but > cause kdamond to exit unexpectedly during parameter application, failing > silently without returning an error to userspace. I'm being more confused. DAMON_SYSFS handles commits synchronously, and return error to user space when it failed, iirc. Am I missing something? > > Solution > ======== > Add an is_power_of_2() check in damon_commit_ctx() to reject invalid > inputs immediately with -EINVAL. If invalid addr_unit already makes damon_commit_ctx() fails and therefore kdamond exit, why we need more check? > > When damon_commit_ctx() fails, the kdamond thread terminates as > designed. Again, I don't get it... Thanks, SJ [...]