From nobody Wed Dec 17 05:46:48 2025 Received: from mail-pg1-f201.google.com (mail-pg1-f201.google.com [209.85.215.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7DA4D16C68C for ; Wed, 24 Jul 2024 19:02:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.215.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721847744; cv=none; b=ONRVtl4rKHv13PXOzp30QI15za4yZtNKRvvCj2d9sl+7QW+oKhOSAUNzdqpfAQ4TvBxDduykrfBE0ayoCuwBy8BJtKx7M4eogFmkwaeO+YvDdKberCbHpUiZ+n8X0vd4lIc0HT5BYRq25tlM6rrcGERTDgNUsIEIsPQR7hDqq/Y= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721847744; c=relaxed/simple; bh=OFk5wDl8xpbdEo44lplWr1p5F7ojENQPq4VGlH1jB9o=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=SVaL3DkLUQAeEJd5OyhbYQHXZSvDyqFQ6PhZsO9U4Y27/H1fhoi6TOKB7ctw470MTI46pOjTBvVBGEZPQJCNooisJ2JXTGpyI2ssjYhQcgCE4tIAquKO7fcmlXhG9GdE8ipI0p93rbRYfNfqvR0mRp/MXOkLGSm2ZQYgYpwk/aU= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--kinseyho.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=XXcCH6fj; arc=none smtp.client-ip=209.85.215.201 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--kinseyho.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="XXcCH6fj" Received: by mail-pg1-f201.google.com with SMTP id 41be03b00d2f7-72c1d0fafb3so105817a12.2 for ; Wed, 24 Jul 2024 12:02:23 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1721847743; x=1722452543; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=AmGz1OUSAYzLu3Mkr9WfTC/ktWFGonkMAhMj+nbyydo=; b=XXcCH6fjno4piANDvv4EwU8SJ6HnglWRFS/PtVQpCDpj6Zpld5fLafQYEpo1YroAnf pjCIr/iyqhFvwvzrR+y9iP0vYtyW/cTY3TYP5yDRnMLZgET0BzBTzTwL0VirxUByu6Y/ wf2lX/XMo/cOPDRXqxYTCw9KqAUmoK/Yu99UE5qkfojeyZ+1BtnYwzHtsnOvP/oCQiHa PRAss8hUyAyYEYArLE+9LfNhMBa67q/TT73UgtYh25nH5gqYf8pQIca3S2B/a4KnFSO3 8hSnnfYMelW6/bvIZcvDvwdiKORBkKppjmK4VwrA2BUpTG+edvB5DYJV+8pl5A7OWjOP WvDg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1721847743; x=1722452543; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=AmGz1OUSAYzLu3Mkr9WfTC/ktWFGonkMAhMj+nbyydo=; b=IgPXO+gKV9IWkP7QqECps/NuFoNQWBGkG3vJEn0B5zPY4GQ+frEvB36xUr4rS/BcIM eBirpuAFJDnlWgWnIqDQ8gfRl2jKUm0AnMw20CFkGglIz2GSs0O1rJzplPSrIq4uJFuv 9tHWIfIx+BO8UV32v3cjwgKUQaAVMjdUcsoMut/rwXQhc8czadth5mSVNei4X2uZ1aK2 Odgt+75WduFFZLeOa2rnv3LLrB+s18GzIQ3K2KwA/K/gJ5B+RC6jWwub3Syud6OOjJ3F rCP9VYtiQE8hFnX9PJlvMsX0mD3M2koV9tUN4dxxHNcYofv5PIHVyOSlf2CAT9XEZZWo BSwg== X-Forwarded-Encrypted: i=1; AJvYcCXdcJuF5BK87MY0PQSBIlS2shIBpzBBPwICeQaQ2LN0Amuw64c176OutiTXNW4GtephoYWbCo2hgaPSht71+hcE7BlEz0UtF8lSM7U6 X-Gm-Message-State: AOJu0YyirNxcO+jcTnXksSfI9drjwHl/kMELXjtAdehfwkLx9HGzy/3C ljfeeeml0S0TJ4gRxO0frZovieO0+IEYkTvALb0KhbNMq+AHi4xbVU55fWjYMA00Pqid5OHEFKy LKBA+plfQpw== X-Google-Smtp-Source: AGHT+IGLvyDW6X3i6jqfX6m7Tz2BzQtjRTiuAHBzI1w6qDTToawljkbGNllzBAuC3KsBrh2qsLZDEguaiP99GA== X-Received: from kinseyct.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:46b]) (user=kinseyho job=sendgmr) by 2002:a17:903:1105:b0:1fb:27bd:82e2 with SMTP id d9443c01a7336-1fed38ccc31mr9895ad.8.1721847742363; Wed, 24 Jul 2024 12:02:22 -0700 (PDT) Date: Wed, 24 Jul 2024 19:02:12 +0000 In-Reply-To: <20240724190214.1108049-1-kinseyho@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240724190214.1108049-1-kinseyho@google.com> X-Mailer: git-send-email 2.45.2.1089.g2a221341d9-goog Message-ID: <20240724190214.1108049-3-kinseyho@google.com> Subject: [PATCH mm-unstable v1 2/4] mm: increment gen # before restarting traversal From: Kinsey Ho To: Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Yosry Ahmed , Roman Gushchin , Kinsey Ho Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" The generation number in struct mem_cgroup_reclaim_iter should be incremented on every round-trip. Currently, it is possible for a concurrent reclaimer to jump in at the end of the hierarchy, causing a traversal restart (resetting the iteration position) without incrementing the generation number. Move the traversal restart such that the generation number is incremented before the restart. Signed-off-by: Kinsey Ho Acked-by: Johannes Weiner --- mm/memcontrol.c | 22 ++++++++++++---------- 1 file changed, 12 insertions(+), 10 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 062bfeee799c..f672bc47c6b5 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -1003,7 +1003,7 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup = *root, root =3D root_mem_cgroup; =20 rcu_read_lock(); - +restart: if (reclaim) { struct mem_cgroup_per_node *mz; =20 @@ -1030,14 +1030,6 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup= *root, for (;;) { css =3D css_next_descendant_pre(css, &root->css); if (!css) { - /* - * Reclaimers share the hierarchy walk, and a - * new one might jump in right at the end of - * the hierarchy - make sure they see at least - * one group and restart from the beginning. - */ - if (!prev) - continue; break; } =20 @@ -1060,8 +1052,18 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup= *root, */ (void)cmpxchg(&iter->position, pos, memcg); =20 - if (!memcg) + if (!memcg) { iter->generation++; + + /* + * Reclaimers share the hierarchy walk, and a + * new one might jump in right at the end of + * the hierarchy - make sure they see at least + * one group and restart from the beginning. + */ + if (!prev) + goto restart; + } } =20 out_unlock: --=20 2.45.2.1089.g2a221341d9-goog