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 0504518A93F for ; Sat, 25 Jul 2026 21:15:30 +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=1785014132; cv=none; b=B2PA2i2vaJjgt+GFtF7VweDOoaIvrKmYAt+pCpoKmIGcHllOtos/4dSdNAiGzeDuDKuAqI30YSc4MIK8/XDkDMWgYP4z/dHuqxQu4xUQT8jv0ZY88aHh8vtpcJu0A352R2A7lny/oqHl1s7sGsQNaqgwTzeLy8ICH7ySvAQfw4o= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785014132; c=relaxed/simple; bh=Nb+XCJgwloBZDTLQwmzyDGjZGWoW1Fj0YLpiQO+g2uk=; h=From:Subject:To:Cc:In-Reply-To:References:Content-Type:Date: Message-Id; b=QjENXIWnNdXIpoOLYtbEt0uW4Afhu3CDFYdt0HJ5K+OJ7KRB+hya7m/ZQqyO6tgDUc1jVGpSOnxPpucx6T3nBvvClSbP86Dk5XYV8xPwlEkRopMPXUuamDCtmyoCJmjgAW+my6IjgOPhBfMecI/EHFYhnTgmzJ3OydCvjyvKdkY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=FnzIPeFt; 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="FnzIPeFt" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8164A1F000E9; Sat, 25 Jul 2026 21:15:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785014130; bh=f2xqTDtd2bcj+/84FiCZ/dk593AOFIIsQlbBkqYrKuk=; h=From:Subject:Reply-To:To:Cc:In-Reply-To:References:Date; b=FnzIPeFtsekD54cIt/v6ikdXxboRPIPv1lScgcIVkGbttLV6Vl2g0XS4N9FBg24+r W05x2yArzVkw7minSJ2fpGKEnoa36RthzM4qrtb/uemn25vOzcWblxCtc8SFEw12sp ssChTNflRqFIT5GB2b7IhfKqEcevmIFe8BmoN0ZyA/49m1KmrGSEPGRffTx0+i/ZHN uW4R/5D6JlTThzHZsmCBB6A4mvIhQdx4Naw0jot2njXCwf3ARm7KddJ4kj2vdQ1bIA 98bCeYhWVsCnhs0yCcYQdbcuUa9U/JylYfOBnSbG2fzd9UE/HiEC1CJ6kKW6KMC/1G nmCEQzhbKEf8g== From: sashiko-bot@kernel.org Subject: Re: [RFC PATCH 08/17] mm/damon/paddr: support damon_prep Reply-To: sashiko-reviews@lists.linux.dev To: "SJ Park" Cc: damon@lists.linux.dev In-Reply-To: <20260725210225.129944-9-sj@kernel.org> References: <20260725210225.129944-1-sj@kernel.org> <20260725210225.129944-9-sj@kernel.org> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Date: Sat, 25 Jul 2026 21:15:30 +0000 Message-Id: <20260725211530.8164A1F000E9@smtp.kernel.org> Precedence: bulk X-Mailing-List: damon@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: Thank you for your contribution! Sashiko AI review found 2 potential issue(= s) to consider: - [High] Double randomization of `r->sampling_addr` silently overwrites the= prepared address when access checks are enabled, leading to an orphaned pr= epared page and evaluation of an unprepared page. - [Medium] Redundant application of `DAMON_PREP_SET_PGIDLE` causes duplicat= e expensive rmap walks for the same folio when multiple probes exist. -- --- Patch [8]: [RFC PATCH 08/17] mm/damon/paddr: support damon_prep --- commit 4bd5ea4d30cf668863712fb6c9fd487551e2b59c Author: SJ Park mm/damon/paddr: support damon_prep This commit implements the prep_probes() callback for physical address=20 operations. It supports the DAMON_PREP_SET_PGIDLE action by unsetting page= =20 table accessed bits and setting the PG_Idle flag. > 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 [ ... ] > +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; [Severity: Medium] Will this result in redundant expensive rmap walks if multiple probes share the same prep action? When iterating over all probes in damon_pa_prep_probes(), this is called for each probe. If a user configures multiple probes with the pgidle_unset filter in a single context, it looks like damon_pa_mkold() will be invoked multiple times for the same sampling_addr, causing duplicate folio rmap traversals. > + 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 =3D damon_rand(ctx, r->ar.start, > + r->ar.end); [Severity: High] Does this conditionally overwrite the sampling address that was already set and prepared? In mm/damon/core.c:kdamond_fn(), prepare_access_checks() and prep_probes() can both be called in sequence: if (!access_check_disabled && ctx->ops.prepare_access_checks) ctx->ops.prepare_access_checks(ctx); if (ctx->ops.prep_probes) ctx->ops.prep_probes(ctx, has_prep); If a user configures a probe with weight=3D0 and a prep action, access_check_disabled is false and has_prep is true. Since has_prep is passed as set_samples, damon_pa_prep_probes() will overwrite the r->sampling_addr that was just prepared by prepare_access_checks(). This would leave the originally prepared page orphaned and cause an unprepared page to be evaluated. > + damon_for_each_probe(p, ctx) > + damon_pa_prep_probes_region(r, p, ctx); > + } > + } > +} --=20 Sashiko AI review =C2=B7 https://sashiko.dev/#/patchset/20260725210225.1299= 44-1-sj@kernel.org?part=3D8