From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5CE823DBA0; Tue, 7 Apr 2026 00:32:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775521922; cv=none; b=qlgFl57fniRxrUUjMKQl9B5yKDcUUOLL786zCCY9RBaG8m6ZtrpPNEnFm3kHTRfUWRUlDVzUATWinmayr0F5eWqPQH85QKGzPk7pMn+xK6vJDe06qg4iXU6mFK/Vj8p1mHJpZTL1c6pWUyKECr3n9FNhj+BdjMzHG+2in73HTl0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775521922; c=relaxed/simple; bh=e6PdU+sFU0K01P//31v0gwLstVAfukUiXGSZ4qXfxgs=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=qGqQ9F4qEE5jB1FMM0dI+2yOhWU5DC4hxO26iQJ6ueOY3dNRDU5fdLU9TPOo5mRnKATcp3QrOSK6S9brNcfzXY+dVrRWrf0zvyB1LNeLMuSgBNnZnPe9ndY/45Cr42UW7bJsGkPJ9iQ70vBSPEptwGP/BELAbUApIuOtbl/thPc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=K8OxJqNe; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="K8OxJqNe" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B655AC4CEF7; Tue, 7 Apr 2026 00:32:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1775521922; bh=e6PdU+sFU0K01P//31v0gwLstVAfukUiXGSZ4qXfxgs=; h=From:To:Cc:Subject:Date:From; b=K8OxJqNeSgov7VyfXY9BqhmgY42pYdzKPlHslDeqPUxlwNM/TjVJaGqePKlGmJ4Av UfaTpT9bxMeoRe5e3nlVBkK3ijzjw0sDqaBXQPyKqB23y45VAnuLvBmMMOVWxjjjQS 5ds7sx1dXy+TfLi4gIw/WcZVqT8g0OPcrbLsl2VggE7gQUH5OxTXJas/Mp+AFBGCEV okZ+PnW7XR/SMhrz2nqp0QQEHTSP0QJ90bqEvC/qpax2mwegf7KFBK7+svdNfl/7eQ yVO8q27a6iXz27ioCEzC5Op0xLKJ0n0QSEqWRc5UxhIgqUrJyf3CrO0q/Yw5rp8Bas 8g1a+bPRuytIw== From: SeongJae Park To: Andrew Morton Cc: SeongJae Park , "# 5 . 16 . x" , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH] mm/damon/core: disallow time-quota setting zero esz Date: Mon, 6 Apr 2026 17:31:52 -0700 Message-ID: <20260407003153.79589-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit When the throughput of a DAMOS scheme is very slow, DAMOS time quota can make the effective size quota smaller than damon_ctx->min_region_sz. In the case, damos_apply_scheme() will skip applying the action, because the action is tried at region level, which requires >=min_region_sz size. That is, the quota is effectively exceeded for the quota charge window. Because no action will be applied, the total_charged_sz and total_charged_ns are also not updated. damos_set_effective_quota() will try to update the effective size quota before starting the next charge window. However, because the total_charged_sz and total_charged_ns have not updated, the throughput and effective size quota are also not changed. Since effective size quota can only be decreased, other effective size quota update factors including DAMOS quota goals and size quota cannot make any change, either. As a result, the scheme is unexpectedly deactivated until the user notices and mitigates the situation. The users can mitigate this situation by changing the time quota online or re-install the scheme. While the mitigation is somewhat straightforward, finding the situation would be challenging, because DAMON is not providing good observabilities for that. Even if such observability is provided, doing the additional monitoring and the mitigation is somewhat cumbersome and not aligned to the intention of the time quota. The time quota was intended to help reduce the user's administration overhead. Fix the problem by setting time quota-modified effective size quota be at least min_region_sz always. The issue was discovered [1] by sashiko. [1] https://lore.kernel.org/20260405192504.110014-1-sj@kernel.org Fixes: 1cd243030059 ("mm/damon/schemes: implement time quota") Cc: # 5.16.x Signed-off-by: SeongJae Park --- Changes from RFC (https://lore.kernel.org/20260405225440.76827-1-sj@kernel.org) - Drop RFC tag. - Rebase to latest mm-hotfixes-unstable. - Slight wordsmithing of the subject. mm/damon/core.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/mm/damon/core.c b/mm/damon/core.c index 3e1890d64d067..3703f62a876b3 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -2228,7 +2228,8 @@ static unsigned long damos_quota_score(struct damos_quota *quota) /* * Called only if quota->ms, or quota->sz are set, or quota->goals is not empty */ -static void damos_set_effective_quota(struct damos_quota *quota) +static void damos_set_effective_quota(struct damos_quota *quota, + struct damon_ctx *ctx) { unsigned long throughput; unsigned long esz = ULONG_MAX; @@ -2254,6 +2255,7 @@ static void damos_set_effective_quota(struct damos_quota *quota) else throughput = PAGE_SIZE * 1024; esz = min(throughput * quota->ms, esz); + esz = max(ctx->min_region_sz, esz); } if (quota->sz && quota->sz < esz) @@ -2290,7 +2292,7 @@ static void damos_adjust_quota(struct damon_ctx *c, struct damos *s) /* First charge window */ if (!quota->total_charged_sz && !quota->charged_from) { quota->charged_from = jiffies; - damos_set_effective_quota(quota); + damos_set_effective_quota(quota, c); } /* New charge window starts */ @@ -2303,7 +2305,7 @@ static void damos_adjust_quota(struct damon_ctx *c, struct damos *s) quota->charged_sz = 0; if (trace_damos_esz_enabled()) cached_esz = quota->esz; - damos_set_effective_quota(quota); + damos_set_effective_quota(quota, c); if (trace_damos_esz_enabled() && quota->esz != cached_esz) damos_trace_esz(c, s, quota); } base-commit: 7c554c59e5a8142c2aea9fd11afbb0fae8876244 -- 2.47.3