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=1794168908; b=33u0cooFekcNQSdK0C+Ix1RC/R7CUIk9hyGG7H5HmjTeIlXY9G7LpUr/219iRPpaowTm arBC0+YxKyavfcTCEg277i67zdtuARair/TJIJe0LyfuUx6AUI1Q/ceqxMDi0Qt9lK1ql CoM26RNrd43mlmL0SrzQ0EZAJzl70nYinCAhN+7BQMS1tA/5duZHXMNQbQm8BuFkNls3o Qqq4cAB1OmZQZJW0WBQaySwIYD+o8X+NkKCGtphLt7gTzjezs/yYoFunStBYFmvJMXeA1 jYQ+KyN9pwhIgq4I6fyCCI+gkKVrmX00M3aORFpxO1IkOkjSMVo5Q0T9IUdf5TsWgpw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794168908; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=uQA9Oy9D6eu6KxEgI1EDIZ+uJxOBHu6oOt+CM7JsTKU=; b=BCbieoaisGVpfVyq+xTLKNmdblfKWpSrxPBppa+bfIQJ/GwFZUaUfbBE+7WN/M+MT2XQ WOkoxiGnNCEFhTcMAsFfH5tPgXfX+gRUoaSXvRtn9zSAA6AkBaLLApEcpzLn+sEOXMBN2 iagXDGZkHp95wYHyYhjkA8zZQmSy8I1nL2VmxDEqtpt05JXcosqDGA2cY1LzmIEafW/oq eHU0zAtT9qSDtSSqdyVgBR1AqOK9TzyCHelPODfHvvcHqCeJ+jAC5M0B2er1dpf+HcLRd 1SMk3Iz3JmlL+xOOlQcJ0xUSQ/LRQeOfG2Soc8/5WP2NKlwa9UpOQ4hBsqnA/gHhmbQ== 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=BZGTGAoS; 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 90482606A320; Sun, 8 Nov 2026 20:15:08 +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=BZGTGAoS Received: by smtp.kernel.org (Postfix) with ESMTPSA id 339741F008A1; Sun, 8 Nov 2026 20:15:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794168908; bh=uQA9Oy9D6eu6KxEgI1EDIZ+uJxOBHu6oOt+CM7JsTKU=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=BZGTGAoSnxPWLIuE6uo4I9+ALy76x261/kivftWKEy78SkHTjJDypwqsxHLAekK/D Y6rUL1pbvzRfbkI4ucKZujclvkVBOlXYLDzyEcWrjBwNSh31LjynpwipS+L6vDHTr3 /rIQlowp9fXr0yKTk/Rk+Md5qR69ujJGJtdI8McQy9XBn0fdKux43BsjEV1IJzuI1K nKVs5rTQabk7j1EbHPw9X1nQrP0o6Dj40e/Fwx7VVA/gGGajQNY7pozXe9nLK0blIj tgbSuw5pEATop+IRLHGTSmnst52qu5zEMy00r8JJMLATRXguHoS9QJpWIHrHVzr0t9 jLUfoQME7suPw== From: SJ Park To: stable@vger.kernel.org Cc: SJ Park , Andrew Morton , Usama Arif , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH 6.6.y 1/3] mm/damon/core: skip applying scheme if region split for quota fails Date: Sun, 8 Nov 2026 12:14:53 -0800 Message-ID: <20261108201456.116824-2-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20261108201456.116824-1-sj@kernel.org> References: <20261108201456.116824-1-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. 6.6.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 b5b6d00d7a3b5..9d4a78deaa06a 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -828,7 +828,7 @@ 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) @@ -1004,7 +1004,8 @@ 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; @@ -1266,15 +1267,17 @@ 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; @@ -1283,6 +1286,7 @@ 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