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=1794087935; b=HgaZTtEStf28m/fv2LvbIYqy2kEDXt60MSJRfwVNXW0TK7wYMUPzoRMct2b/fxgk9oNN 1mk4IETTc3XA1Y5tXjjN1VyeK/JTWjHxMEL0lyBmlzlNR9/LscOKrH0ljzMPf5c6EnHj2 2mrai5cp+1qXb7bpmR0pN18OxYCcPFyWaHR3Zou6AjaWf6QhEuDOIPlVkJeS0c9QLTwR4 1EFCYuSFvcK8FsoWRlhHNXLIQSEkyBGQdH8Da8OeczBevkji6fCQ1c4BnoAnd+jKl+GKj tBgVT2l93xL0R7XxGu2Z+1L3Vn2wXBgZsNg1Jn11Xfo0TPm5xK7auEwf0K8YvN0a33g== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794087935; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=Jg6uYRNhV7mTrgb91kiVKd41vY7ff4cg96iZM39MthE=; b=28Bi3Ahg/0moaUL6ZWO9FJQ6mep5gJnWfTK6/vMkDr6IxRDdodu4Uq0dWLk+eeCpp0pF 7KrmU98KHvsfmZbZ61C8+V9XiwpTVHYi3nYWdlZpSnIAVrDtAekKwuH0cUATY5cGdkFfZ 2T+VP+qb3XCbD8gIx29Y1ABz/li8rLIL0DbH/Mx0B2+mMmS5e32uy+GwYIl3BBNFkReS3 t0oip053hVuTs+NIU6WZ/ZLfzjhacjnBH+cz5Ivh/2bwoXE9eC4cNRalH2MbUSuPc2jmA qbMJQ+A8DeJtme8dk+ajpVytkwdlpFts+fSHFKvgZXJGneoe810xeTvv2c3nyIXUIpw== 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="oL/zu0XQ"; 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 CC9E9606A32C; Sat, 7 Nov 2026 21:45:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=oL/zu0XQ Received: by smtp.kernel.org (Postfix) with ESMTPSA id 60A641F008A2; Sat, 7 Nov 2026 21:45:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794087934; bh=Jg6uYRNhV7mTrgb91kiVKd41vY7ff4cg96iZM39MthE=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=oL/zu0XQFZaVfByvORZm31uzlL1kH9iZIQ5kdPtCh6MIXLDcb95w1Y8QfuHey5/fQ WfhE2Uv3CrpUZO+yBgilHI+A9zN2eQu0oO+XijYO+CkTsztVUvrk1IphCLlJMRhJAl 2vaqWMhpdt0KQGtAmmC9hAjskXzZmnJWJQfE2OYLBCEIklZff4LKXlmY3T3NlnyEbd Ow3TNupoUfoJNfTIYk6CfPqgZibk4yk5G3uXFZax64L8sS8i7UvdGok6ElA5k8L8So g4cKAtJ4K7aIaKIvNjizyxxL8V6ArKR6vfrs1oyxLsRcEBNdS6qsvabpy2Ni4MTslt PlTVyKZIQO6KQ== From: SJ Park To: Cc: SJ Park , stable@vger.kernel.org, Andrew Morton , Usama Arif , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [RFC PATCH 6.12.y 1/5] mm/damon/core: skip applying scheme if region split for quota fails Date: Sat, 7 Nov 2026 13:45:20 -0800 Message-ID: <20261107214525.304638-2-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20261107214525.304638-1-sj@kernel.org> References: <20261107214525.304638-1-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 Patch series "mm/damon: fix DAMOS bugs in core, paddr and vaddr". Fix misc bugs of DAMOS. Patch 1 makes DAMOS less stress memory allocator under extreme situation. Patches 2 and 3 fix wrong folios walking in DAMON_PADDR. Patches 4 and 5 fix wrong folios walking in DAMON_VADDR. Patches 6-8 handle extreme and unlikely memory situations that can cause divide by zero and underflow. All bugs are discovered by Sashiko. This patch (of 8): damos_apply_scheme() splits a region and apply the action to the subregion if it is needed for not violating the quota. The split operation (damon_split_region_at()) could fail for allocation failure. In the case, the quota could be violated. From the user's perspective, DAMOS becomes more aggressive than expected under the extreme situation. Handle the failure. The user impact is not critical. The failure of damon_split_region_at() is unlikely since it is arguably too small to fail. Also DAMOS being aggressive is limited to the single region. Users can set min_nr_regions to set the maximum size of each region. If it is reasonably set, the transient overhead shouldn't be critical. The issue was discovered [1] by Sashiko. 6.12.y porting notes. Modify damon_split_region_at() to return failures. It is a part of commit c60874860762 ("mm/damon/core: handle region split failure in apply_min_nr_regions()"). Without it, build fails. Link: https://lore.kernel.org/20260901131850.98037-1-sj@kernel.org Link: https://lore.kernel.org/20260901131850.98037-2-sj@kernel.org Link: https://lore.kernel.org/20260718171523.87547-1-sj@kernel.org [1] Fixes: 2b8a248d5873 ("mm/damon/schemes: implement size quota for schemes application speed control") Signed-off-by: SJ Park Signed-off-by: Andrew Morton Cc: Usama Arif Cc: # 5.16.x (cherry picked from commit 90c2fa6adfed7abe0935506a43cdff3a05c1fff0) Signed-off-by: SJ Park --- mm/damon/core.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) diff --git a/mm/damon/core.c b/mm/damon/core.c index 81d44e41de210..6ef77741b783b 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -1266,7 +1266,7 @@ static void kdamond_reset_aggregated(struct damon_ctx *c) } } -static void damon_split_region_at(struct damon_target *t, +static int damon_split_region_at(struct damon_target *t, struct damon_region *r, unsigned long sz_r); static bool __damos_valid_target(struct damon_region *r, struct damos *s) @@ -1470,7 +1470,8 @@ static void damos_apply_scheme(struct damon_ctx *c, struct damon_target *t, DAMON_MIN_REGION); if (!sz) goto update_stat; - damon_split_region_at(t, r, sz); + if (damon_split_region_at(t, r, sz)) + goto update_stat; } if (damos_filter_out(c, t, r, s)) return; @@ -1861,15 +1862,17 @@ static void kdamond_merge_regions(struct damon_ctx *c, unsigned int threshold, * * r the region to be split * sz_r size of the first sub-region that will be made + * + * Return: 0 on success, negative error code otherwise. */ -static void damon_split_region_at(struct damon_target *t, +static int damon_split_region_at(struct damon_target *t, struct damon_region *r, unsigned long sz_r) { struct damon_region *new; new = damon_new_region(r->ar.start + sz_r, r->ar.end); if (!new) - return; + return -ENOMEM; r->ar.end = new->ar.start; @@ -1879,6 +1882,7 @@ static void damon_split_region_at(struct damon_target *t, new->nr_accesses = r->nr_accesses; damon_insert_region(new, r, damon_next_region(r), t); + return 0; } /* Split every region in the given target into 'nr_subs' regions */ -- 2.47.3