From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 63E2B3A3815 for ; Tue, 28 Jul 2026 04:57:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785214634; cv=none; b=aLjU9HJyPr+QZgS0tLqsu5mIRhRV7KkbVvuDyURbbMyGlR8VmezVxlitWA46YNHl8qXCqx2sIz3XRuWMhdoZZuhliRe5ISDSOpuWrGjdDR6p1ESOLu+Vx34qJMGu7/aKQfi6TeirCt1VxNHDa5rWufqoC9bs8GkJJa1jd1J1TOI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785214634; c=relaxed/simple; bh=8GlkwnQLXbaVWEOh5tXoRWSpQhWuW18sHaMniAGJV7s=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=XIJvpBcE/Up2IJRWmUrMWPBhI9tQ+7JqxW31eiAqtaD9Z2pbJJ39DoYjDnR5GauzBdv30V9mtVmrOuLFFWmE4e35kDaEnQaw7YuBRlYaE4UMa2b4sr2dXenGLY9wtRJT1m7GqR+VOm3C8aeTX1PsqNgVzyTaXPtPmSh/K6vgG4g= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=nSJyh0JN; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="nSJyh0JN" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CE0D91F000E9; Tue, 28 Jul 2026 04:57:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785214632; bh=bk87TJYg/W7+I5qmYx+qdRFQMVvRhK4t0qrE9QaOxdI=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=nSJyh0JNEQG8q/d5F00uCF8HV+v+GCpV29j5IHlYW4iknx/tqxW3ZVL4cd8o9enQ9 bjwtA+H87qaQ6ZZt3g2LREgdr6/o+kOVFgA/ev6R1+xplP7f18B0hxJmKeYpuoPSOd jat5knqD0dOG1dqjne72CZ4NVrpmtke0mlXO78pAgAl4oqX6107JYELCykwHxOlkgm XzRxawrvCMkQqNWdfDgg9ITKXdevF3LEw1PyTxlQsX5mHCVU0K2rIceczwNYAtaOgQ 2xjpf3gdvP2/gThQ3Nm91xi+nQgHz3VUcxDYrmr/7vNPBwbJj/ksZeMRLTslQFaUIW LgfIUri7d4QbQ== From: SJ Park To: sashiko-bot@kernel.org Cc: SJ Park , damon@lists.linux.dev Subject: Re: [RFC PATCH v2.2 08/17] mm/damon/paddr: support damon_prep Date: Mon, 27 Jul 2026 21:56:59 -0700 Message-ID: <20260728045700.189863-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260728042457.48D531F000E9@smtp.kernel.org> References: Precedence: bulk X-Mailing-List: damon@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On Tue, 28 Jul 2026 04:24:56 +0000 sashiko-bot@kernel.org wrote: > Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider: > - [High] damon_pa_prep_probes() executes prep actions redundantly and ignores probe filters, causing excessive rmap walks and global LRU degradation. > -- > > --- Patch [8]: [RFC PATCH v2.2 08/17] mm/damon/paddr: support damon_prep --- > commit 5d5b08fab7578294743c8bbbba6c3bfa16036115 > Author: SJ Park > > mm/damon/paddr: support damon_prep > > This commit implements the damon_operations->prep_probes() callback to > support the DAMON_PREP_SET_PGIDLE action. It unsets page table accessed > bits and sets the PG_Idle flag, similar to what is done for access check > preparation. > > > diff --git a/mm/damon/paddr.c b/mm/damon/paddr.c > > index 199de1463fa06..8d8fcd1369e56 100644 > > --- a/mm/damon/paddr.c > > +++ b/mm/damon/paddr.c > > [ ... ] > > > @@ -105,6 +105,40 @@ static unsigned int damon_pa_check_accesses(struct damon_ctx *ctx) > > return max_nr_accesses; > > } > > > > +static void damon_pa_prep_probes_region(struct damon_region *r, > > + struct damon_probe *probe, struct damon_ctx *ctx) > > +{ > > + struct damon_prep *p; > > + > > + damon_for_each_prep(p, probe) { > > + switch (p->action) { > > + case DAMON_PREP_SET_PGIDLE: > > + damon_pa_mkold(damon_pa_phys_addr(r->sampling_addr, > > + ctx->addr_unit)); > > + break; > > + default: > > + break; > > + } > > + } > > +} > > + > > +static void damon_pa_prep_probes(struct damon_ctx *ctx, bool set_samples) > > +{ > > + struct damon_target *t; > > + struct damon_region *r; > > + struct damon_probe *p; > > + > > + damon_for_each_target(t, ctx) { > > + damon_for_each_region(r, t) { > > + if (set_samples) > > + r->sampling_addr = damon_rand(ctx, r->ar.start, > > + r->ar.end); > > + damon_for_each_probe(p, ctx) > > + damon_pa_prep_probes_region(r, p, ctx); > > [Severity: High] > Does this code redundantly execute damon_pa_mkold() and ignore probe filters? > > In kdamond_fn(), if standard access checks are enabled, both > prepare_access_checks() and prep_probes() can execute on the same tick: > > if (!access_check_disabled && ctx->ops.prepare_access_checks) > ctx->ops.prepare_access_checks(ctx); > if (do_prep) > ctx->ops.prep_probes(ctx, access_check_disabled); > > Because prepare_access_checks() also calls damon_pa_mkold(), the subsequent > iteration over all probes here unconditionally calls it again on the exact same > sampling address for every probe configured with DAMON_PREP_SET_PGIDLE. Since > damon_pa_mkold() performs a costly rmap_walk, this multiplies the overhead. That's true, but no problem. Sane users may not use the classic monitoring with set_pgidle prep. > > Additionally, this loop does not evaluate probe filters (such as MEMCG or > ANON) before applying prep actions. Could this blindly clear the accessed bit > for all sampled pages globally, artificially aging pages that the user > explicitly excluded and degrading system-wide memory reclaim decisions? Yes, and that's the intended behavior. If user asks to set pgidle, DAMON sets pgidle. > > > + } > > + } > > +} > > + > > -- > Sashiko AI review ยท https://sashiko.dev/#/patchset/20260728041242.187380-1-sj@kernel.org?part=8 Thanks, SJ