From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1792870440; b=IEsxyColVsG47NJTnwlSpxXbSI9AHWi7qlhCft71wjrXpw3BVVmefgNLxu8Nb+Ya65Ng 50svHPPy4Ahth5m6GH2ipYklI6Zbzi9XBRTnXdWMkbVUaU8OAW+hQZJpFxY1ZYkGpCuvC dXuICYmgeq2GhXnIyhlDCMXF/v9Me1XjZ/6ColwswwCiOPQ0ud4AOzdTBW+ZwP4wzeGbS s2YjuhvsAbzikEVeOP5VZ1kpPzzYoGTiMM98G03dYJEKkheVwbQemCTIfyfgARDc4c8nC wpUybE1pYTZobNJZtI0do0Vmkjxychm2hORs9h33X8N4yoYU8cyBgRR6oxMwbVRFVQQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1792870440; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=HjEsKHyDFKj7HHX5WZLrUS4CLP7wbTWvbErAlhp6Z7k=; b=wgzRSbwXjMOWXVLsgC0zq0r0mRcbelzu/WJ8bdqo8Z8QTh8Z05DnjKwLTXlCPNKf1HET M2QKmIYcG57+HSAzRIZy4IdapVeCNAShPssabOfSRY8ey/5YX0e3VXUHuaQHZG+0FmlGB Xwt6lVOwGN2PP1fyNcL9K/tBuDa3DxQuhHNDheNlox90u9XEEL3FKEfCzuSsPP7FSw0cy EhvRABMj6ftGmce3+PKE5hRPY3LEmNHs4k1BjCAR7lIh2iuzin+X+kfwIye+9EKKZH6dQ 7lkPKut6pNbjyZrLN4dmgaPU7lxwTe1DRKkCXVEigH+CNe/zWxWWX8S0iNfgp+ytQiA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=EfoDNYpT; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7D1B6606A32F; Sat, 24 Oct 2026 19:34:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=EfoDNYpT Received: by smtp.kernel.org (Postfix) with ESMTPSA id F2B951F01825; Sat, 24 Oct 2026 19:33:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1792870440; bh=HjEsKHyDFKj7HHX5WZLrUS4CLP7wbTWvbErAlhp6Z7k=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=EfoDNYpTX4r7251gPD043Z1N82zWoBSTl5aNvZtonOA4CjNZ3L1eLdV95xz2RfATx 2faEgGwhj0NbSZZr7VkX0Q8X4/3r4FCxr5Zh6LMv2YSYHUARHCPMkCR59uwDPDlZmc 1jQENf/ehnrpbH94glJSmQAZtY2FGFwBYC7vVXrCMTg6LZaHEMBRQ/7JFdgRTK/68q U0NH2cctz0L7JkiXtwHihVPr3EyRbK4hBlBdndEytlIS2aY/x+Geg3w1oWM56MTmaD G3g9mTg+opI83yKo93OuXV0A83hfzIYdrCe0ltAbLOaWcB72/prR4m/cUlsm2mRn+O saIR+PzEetDKg== From: SJ Park To: Cc: SJ Park , stable@vger.kernel.org, Andrew Morton , Jiayuan Chen , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [RFC PATCH 3/3] mm/damon/core: move static variable rotation to damon_ctx Date: Sat, 24 Oct 2026 12:33:49 -0700 Message-ID: <20261024193351.87130-4-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20261024193351.87130-1-sj@kernel.org> References: <20261024193351.87130-1-sj@kernel.org> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit damon_split_some_reigons() uses a static variable, rotation, to remember how many times it was called. It is again used to determine fair selection of regions to split. Since it is a static variable, it can be indeterministic and therefore less fair. The user impact is not critical. No crash, no leak. DAMON's best-effort and indeterministic monitoring accuracy could be slightly more indeterministic when multiple kdamonds are used in parallel. Fix the problem by moving the static variable into the damon_ctx struct. Fixes: 1a582e6e0174 ("mm/damon/core: split a fraction of regions when nr_regions exceeds max/2") Cc: # 7.3.x Closes: https://sashiko.dev/#/bug/linux-eebfcdde-2881-48ef-8df1-e2019d2a47f2 Signed-off-by: SJ Park --- include/linux/damon.h | 5 +++++ mm/damon/core.c | 5 +++-- 2 files changed, 8 insertions(+), 2 deletions(-) diff --git a/include/linux/damon.h b/include/linux/damon.h index cb6a50032a1eb..380f9cf6ddd82 100644 --- a/include/linux/damon.h +++ b/include/linux/damon.h @@ -963,6 +963,11 @@ struct damon_ctx { * for more details. */ unsigned long last_nr_regions; + /* + * number of damon_split_some_regions() invocations for this context. + * Read damon_split_some_regions() for more details. + */ + unsigned long region_split_rotation; }; /* Get a random number in [@l, @r) using @ctx's lockless PRNG. */ diff --git a/mm/damon/core.c b/mm/damon/core.c index 09722257ce736..73b571b429cb3 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -3753,12 +3753,13 @@ static void damon_split_regions_of(struct damon_ctx *ctx, static void damon_split_some_regions(struct damon_ctx *ctx, unsigned long split_step) { - static unsigned long rotation; struct damon_target *t; struct damon_region *r, *next; - unsigned long offset = rotation++ % split_step; + unsigned long offset; unsigned long idx = 0; + offset = ctx->region_split_rotation++ % split_step; + damon_for_each_target(t, ctx) { damon_for_each_region_safe(r, next, t) { unsigned long sz_region, sz_sub; -- 2.47.3