From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pl1-f171.google.com (mail-pl1-f171.google.com [209.85.214.171]) (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 3FD2D168D0 for ; Tue, 3 Sep 2024 22:39:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.171 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725403189; cv=none; b=lcE/AJXtoXhJODBjjRnZ0NEP3Tf3vhEC6CRzqjBSxKZVamPpvTXGOq2tEjDzktKYMNdU78TnaSgukuZAJL/ilhHOkSlaPcDSESZjvrTJer+fTC1zYiPkOk/FF3qcYQmPNskiIt4D471AW7Ey+Bqn1ihEpFIrAI8gAd/HP3x/QRw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725403189; c=relaxed/simple; bh=KeS+/H/ggeQdORa2PHv0xcObmCvkTFDDKzaYSlN5KcM=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version:Content-Type; b=cGmMFDepl7qCKmv7ItC69wLH7Vjn5mJM75WnxzuuujS23wY6nS5aytktmjqltdgQFN9Ots0aKTLbBAwA0XnSdMNpcn356SY9uce91AoN9/jkPnwEAF0tZGj9S2Vc93iL0R2FnNmvPgPPduqQV1aT4SR3Pwa6/6cT9SF3BJN4ixI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=hyYlSsdf; arc=none smtp.client-ip=209.85.214.171 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="hyYlSsdf" Received: by mail-pl1-f171.google.com with SMTP id d9443c01a7336-2055f630934so21202015ad.1 for ; Tue, 03 Sep 2024 15:39:48 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1725403187; x=1726007987; darn=lists.linux.dev; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=lJzEDZ6Y41Cwm+nItw4ApEDZvLrm6Zf0G+Ovt54oSKM=; b=hyYlSsdfMf8+AM01WJ0rI4N3dKPO40CBkznMu0whmneTP6HQyUygD2UBG/rKG1ASbF kcs2NqOOVRc/tnE8auXpkQLdmhzpKs+zVDlb//HW1iULEm5o3LI0MPYWjsTs8Gbx5Ige s0+kECtcoNQlNJ7/ZSpHVEU9zSo8jiupXm/XBz39P2PpBvOCgFsYaaRoDGXLZJKzWFH0 9AqxQJOC7YQxUMUPc53i0wzRCTle4tyo8uGOtV6RgHoOEhHcM+SPII2Ggu98vwiWyZyo 4CZ7vGBb1MIAENjXyOmK8VQlfAPsdlLcdDthkoA4ikgCO9GzwhOApZgmOrb9LLdzh8ow GmNA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1725403187; x=1726007987; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=lJzEDZ6Y41Cwm+nItw4ApEDZvLrm6Zf0G+Ovt54oSKM=; b=mj2KA7NZQZ8JyU1D3F/Q7cIdgm9YLiphypM7DfRL69COEX81FwaO2lSEjqIQJj1RDV 4aaqZqJ2JyDbzYeIxstiBeXD3Mo3dmz0wYkkTortkWZTxHrpxMTHT2x3pOvkA+S6e40M lj1n4/bajg1VylqowTxiQ4UdJwGJ/9LbaR46D5AAh6Y1ICEaoHCrFe/XIwV6iQ+7RLHU WFEZFOZd+QKBEylgv4oDFOkZ17EATFg8E/uRr4J27YYtLX7Bp0CVXjYlPYPGqxmyNHR5 AQzPb13Cfi4Q0/e7ldYxMzT6Whd+rtLKdVYsJOH5M8WHd9gc7PAMmzh0F/FwUkZqfXpE e4Pg== X-Forwarded-Encrypted: i=1; AJvYcCUg+edgKgPQDDAJoAPW33eKz8p2bZ9cXGeK0c6RW3CHDMHmIqjAk/qjqy8GDutouEgMigr/UdahjXqxUZxf8A==@lists.linux.dev X-Gm-Message-State: AOJu0Yxa2feF8o4PYSgncu9HKivUL17c9dIK+RNG1SVykhE1N8aXldz6 rdfcR8hMK35rtUdYFCxhSiIQ2A8hbrkPSk+5D4VqUK3tx+EDo0+v X-Google-Smtp-Source: AGHT+IF4JZ9uttpCEjhGk+KRVirtmc6UBRZKXBbOBrpMJWbwoF0ZbezJXFzPRsbM0ocaAmPCoeH3ig== X-Received: by 2002:a17:903:2b04:b0:205:51ee:b81e with SMTP id d9443c01a7336-20551eebb28mr131826195ad.15.1725403187460; Tue, 03 Sep 2024 15:39:47 -0700 (PDT) Received: from Barrys-MBP.hub ([2407:7000:8942:5500:3dfb:fdbe:2749:2520]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-206aea55789sm3007825ad.217.2024.09.03.15.39.40 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Tue, 03 Sep 2024 15:39:47 -0700 (PDT) From: Barry Song <21cnbao@gmail.com> To: mhocko@suse.com Cc: 21cnbao@gmail.com, 42.hyeyoo@gmail.com, akpm@linux-foundation.org, cl@linux.com, david@redhat.com, hailong.liu@oppo.com, hch@infradead.org, iamjoonsoo.kim@lge.com, laoar.shao@gmail.com, linux-mm@kvack.org, penberg@kernel.org, rientjes@google.com, roman.gushchin@linux.dev, torvalds@linux-foundation.org, urezki@gmail.com, v-songbaohua@oppo.com, vbabka@suse.cz, virtualization@lists.linux.dev Subject: Re: [PATCH v4 3/3] mm: warn about illegal __GFP_NOFAIL usage in a more appropriate location and manner Date: Wed, 4 Sep 2024 10:39:35 +1200 Message-Id: <20240903223935.1697-1-21cnbao@gmail.com> X-Mailer: git-send-email 2.39.3 (Apple Git-146) In-Reply-To: References: Precedence: bulk X-Mailing-List: virtualization@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 Mon, Sep 2, 2024 at 7:58 PM Michal Hocko wrote: > > On Sat 31-08-24 08:28:23, Barry Song wrote: > > From: Barry Song > > > > Three points for this change: > > > > 1. We should consolidate all warnings in one place. Currently, the > >    order > 1 warning is in the hotpath, while others are in less > >    likely scenarios. Moving all warnings to the slowpath will reduce > >    the overhead for order > 1 and increase the visibility of other > >    warnings. > > > > 2. We currently have two warnings for order: one for order > 1 in > >    the hotpath and another for order > costly_order in the laziest > >    path. I suggest standardizing on order > 1 since it’s been in > >    use for a long time. > > > > 3. We don't need to check for __GFP_NOWARN in this case. __GFP_NOWARN > >    is meant to suppress allocation failure reports, but here we're > >    dealing with bug detection, not allocation failures. So replace > >    WARN_ON_ONCE_GFP by WARN_ON_ONCE. > > > > Suggested-by: Vlastimil Babka > > Signed-off-by: Barry Song > > Acked-by: Michal Hocko > > Updating the doc about order > 1 sounds like it would still fall into > the scope of this patch. I don not think we absolutely have to document > each unsupported gfp flags combination for GFP_NOFAIL but the order is a > good addition with a note that kvmalloc should be used instead in such a > case. Hi Andrew, If there are no objections from Michal and David, could you please squash the following: >From fc7a2a49e8d0811d706d13d2080393274f316806 Mon Sep 17 00:00:00 2001 From: Barry Song Date: Wed, 4 Sep 2024 10:26:19 +1200 Subject: [PATCH] mm: also update the doc for __GFP_NOFAIL with order > 1 Obviously we only support order <= 1 __GFP_NOFAIL allocation and if someone wants larger memory, they should consider using kvmalloc() instead. Suggested-by: David Hildenbrand Suggested-by: Michal Hocko Signed-off-by: Barry Song --- include/linux/gfp_types.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/include/linux/gfp_types.h b/include/linux/gfp_types.h index 4a1fa7706b0c..65db9349f905 100644 --- a/include/linux/gfp_types.h +++ b/include/linux/gfp_types.h @@ -253,7 +253,8 @@ enum { * used only when there is no reasonable failure policy) but it is * definitely preferable to use the flag rather than opencode endless * loop around allocator. - * Using this flag for costly allocations is _highly_ discouraged. + * Allocating pages from the buddy with __GFP_NOFAIL and order > 1 is + * not supported. Please consider using kvmalloc() instead. */ #define __GFP_IO ((__force gfp_t)___GFP_IO) #define __GFP_FS ((__force gfp_t)___GFP_FS) -- 2.34.1 > > > --- > >  mm/page_alloc.c | 50 ++++++++++++++++++++++++------------------------- > >  1 file changed, 25 insertions(+), 25 deletions(-) > > > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > index c81ee5662cc7..e790b4227322 100644 > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -3033,12 +3033,6 @@ struct page *rmqueue(struct zone *preferred_zone, > >  { > >       struct page *page; > > > > -     /* > > -      * We most definitely don't want callers attempting to > > -      * allocate greater than order-1 page units with __GFP_NOFAIL. > > -      */ > > -     WARN_ON_ONCE((gfp_flags & __GFP_NOFAIL) && (order > 1)); > > - > >       if (likely(pcp_allowed_order(order))) { > >               page = rmqueue_pcplist(preferred_zone, zone, order, > >                                      migratetype, alloc_flags); > > @@ -4175,6 +4169,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, > >  { > >       bool can_direct_reclaim = gfp_mask & __GFP_DIRECT_RECLAIM; > >       bool can_compact = gfp_compaction_allowed(gfp_mask); > > +     bool nofail = gfp_mask & __GFP_NOFAIL; > >       const bool costly_order = order > PAGE_ALLOC_COSTLY_ORDER; > >       struct page *page = NULL; > >       unsigned int alloc_flags; > > @@ -4187,6 +4182,25 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, > >       unsigned int zonelist_iter_cookie; > >       int reserve_flags; > > > > +     if (unlikely(nofail)) { > > +             /* > > +              * We most definitely don't want callers attempting to > > +              * allocate greater than order-1 page units with __GFP_NOFAIL. > > +              */ > > +             WARN_ON_ONCE(order > 1); > > +             /* > > +              * Also we don't support __GFP_NOFAIL without __GFP_DIRECT_RECLAIM, > > +              * otherwise, we may result in lockup. > > +              */ > > +             WARN_ON_ONCE(!can_direct_reclaim); > > +             /* > > +              * PF_MEMALLOC request from this context is rather bizarre > > +              * because we cannot reclaim anything and only can loop waiting > > +              * for somebody to do a work for us. > > +              */ > > +             WARN_ON_ONCE(current->flags & PF_MEMALLOC); > > +     } > > + > >  restart: > >       compaction_retries = 0; > >       no_progress_loops = 0; > > @@ -4404,29 +4418,15 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, > >        * Make sure that __GFP_NOFAIL request doesn't leak out and make sure > >        * we always retry > >        */ > > -     if (gfp_mask & __GFP_NOFAIL) { > > +     if (unlikely(nofail)) { > >               /* > > -              * All existing users of the __GFP_NOFAIL are blockable, so warn > > -              * of any new users that actually require GFP_NOWAIT > > +              * Lacking direct_reclaim we can't do anything to reclaim memory, > > +              * we disregard these unreasonable nofail requests and still > > +              * return NULL > >                */ > > -             if (WARN_ON_ONCE_GFP(!can_direct_reclaim, gfp_mask)) > > +             if (!can_direct_reclaim) > >                       goto fail; > > > > -             /* > > -              * PF_MEMALLOC request from this context is rather bizarre > > -              * because we cannot reclaim anything and only can loop waiting > > -              * for somebody to do a work for us > > -              */ > > -             WARN_ON_ONCE_GFP(current->flags & PF_MEMALLOC, gfp_mask); > > - > > -             /* > > -              * non failing costly orders are a hard requirement which we > > -              * are not prepared for much so let's warn about these users > > -              * so that we can identify them and convert them to something > > -              * else. > > -              */ > > -             WARN_ON_ONCE_GFP(costly_order, gfp_mask); > > - > >               /* > >                * Help non-failing allocations by giving some access to memory > >                * reserves normally used for high priority non-blocking > > -- > > 2.34.1 > > -- > Michal Hocko > SUSE Labs Thanks Barry