From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-170.mta0.migadu.com (out-170.mta0.migadu.com [91.218.175.170]) (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 31F5A181334 for ; Tue, 14 Jul 2026 11:31:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.170 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784028698; cv=none; b=YBQ8geX8jl6u2jjHfo72MGhTqSlCcZR+6GMgaMiZUUvc17mtnRnwYDRqMzMjOfc8Pb8voRItHJQZm2MRBtuk5ZTRRfJm0jvi/IOyVfwXaeW2qL7TRJdluWktE3GHEFUKBjwbf2n4mJjSQDRlP5zuNs3gXSU7LwKie4tNnkGbRSA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784028698; c=relaxed/simple; bh=TlmowfgjlYhKKe5E5aDr1vq0P2d3pioFecjrJCqWABc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=tdpbmku/1pQPbyoneAnEeHO4eJMbSnqZVHfzIUffx3kCktzvj0HGcSb9APTLVYfG/WLpx7v5H9vvhxonI3g25eoHoZ96q5XPQK1PlVlHGC6ZXOmaPXyrdYbJ2MvOr3RYL4jScmyyRtYMi7Ebhv75FloEAmR40eolT3evMvftvAQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=aubsTbCz; arc=none smtp.client-ip=91.218.175.170 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="aubsTbCz" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1784028683; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=zwhrkQgNNnztcrozTTZGeAnrDC8vAtQeya0vh3r35g4=; b=aubsTbCz2J03ebsHx5YMNPz+vCnRTn2SVDUHzV4RWAcoPSGngHtReBCmi1/XyTh4KGbt8A 72hx/ld7+39lC45i4jqGr1WlT4lLcu/Rkvyu7Xj+/pjRSGYywHARH9pvG50tCZrLWq5EMW pyoqFG4tdKTLCW8zpowzsqFvlGyB/GM= Date: Tue, 14 Jul 2026 19:31:05 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH 1/2] memcg: move mem_cgroup_swappiness to memcontrol.h To: Barry Song Cc: Andrew Morton , Johannes Weiner , Michal Hocko , Roman Gushchin , Shakeel Butt , Muchun Song , Chris Li , Kairui Song , David Hildenbrand , Yuanchu Xie , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Ridong Chen References: <20260711091157.306070-1-ridong.chen@linux.dev> <20260711091157.306070-2-ridong.chen@linux.dev> <87dc4105-b98b-4541-bafe-c0adfbf58836@linux.dev> <0545ee70-b0a0-4a93-ac2c-3e84ff504e5a@linux.dev> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Ridong Chen In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 7/14/2026 6:21 PM, Barry Song wrote: > On Tue, Jul 14, 2026 at 3:43 PM Ridong Chen wrote: >> >> >> >> On 7/14/2026 9:48 AM, Barry Song wrote: >>> On Tue, Jul 14, 2026 at 9:43 AM Barry Song wrote: >>>> >>>> On Tue, Jul 14, 2026 at 9:20 AM Ridong Chen wrote: >>>>> >>>>> >>>>> >>>>> On 7/13/2026 11:08 PM, Barry Song wrote: >>>>>> On Sat, Jul 11, 2026 at 5:12 PM Ridong Chen wrote: >>>>>>> >>>>>>> From: Ridong Chen >>>>>>> >>>>>>> The per-memcg swappiness knob is v1-only; v2 always uses global >>>>>>> vm_swappiness and ignores the per-cgroup field. >>>>>>> >>>>>>> Guard memcg->swappiness with CONFIG_MEMCG_V1, and move the helper >>>>>>> to memcontrol.h where it belongs. >>>>>>> >>>>>>> No functional change for v1; v2-only kernels drop the unused field. >>>>>>> >>>>>>> Signed-off-by: Ridong Chen >>>>>>> Acked-by: Johannes Weiner >>>>>> >>>>>> Reviewed-by: Barry Song >>>>>> >>>>>> With some nits. >>>>>> >>>>>>> --- >>>>>> [...] >>>>>>> struct mem_cgroup_per_node *nodeinfo[]; >>>>>>> @@ -365,6 +366,9 @@ enum objext_flags { >>>>>>> >>>>>>> #define OBJEXTS_FLAGS_MASK (__NR_OBJEXTS_FLAGS - 1) >>>>>>> >>>>>>> +/* Defined in mm/vmscan.c; used by mem_cgroup_swappiness(). */ >>>>>>> +extern int vm_swappiness; >>>>>> >>>>>> This is a bit unusual. I'm not sure whether mm/swap.h would be >>>>>> a more appropriate place for this. >>>>>> >>>>> Thank you for your reply. >>>>> >>>>> The vm_swappiness variable is not utilized within mm/swap.c. >>>>> Furthermore, since memcontrol.h does not include swap.h, retaining the >>>>> extern int vm_swappiness declaration in mm/swap.h will result in a >>>>> compilation failure. >>>> >>>> If this is the case, it still seems better to keep >>>> extern int vm_swappiness in include/linux/swap.h. >>>> >>>> Then we don't need the comment: >>>> /* Defined in mm/vmscan.c; used by mem_cgroup_swappiness(). */ >>>> >>>> It also makes it clearer that vm_swappiness is an extern variable >>>> belonging to the swap module, rather than the memcontrol module. >>> >>> BTW, if mem_c_group_swappiness() and vm_swappiness are only used >>> within mm/, could all of these be moved to mm/swap.h and >>> mm/internal.h instead? >>> >>> We are making a big effort to move many unrelated things out of >>> include/linux/swap.h recently. Could you check? >>> >>> https://lore.kernel.org/linux-mm/20260708-ch-swap-series-plus-folio-lru-cleanup-v9-0-2bc72b4f8730@gmail.com/ >> >> Good suggestion. Moving them to mm/internal.h makes sense. Will update >> in the next version. > > Either mm/swap.h or mm/internal.h. > vm_swappiness probably belongs in mm/swap.h rather than > mm/internal.h, right? > > BTW, I am not particularly eager about this cleanup; > it could be done later as a separate patch. > > If you decide not to do the cleanup, I think it would be better to > leave "extern int vm_swappiness" in include/linux/swap.h rather than > declaring it in include/linux/memcontrol.h? I noticed that some swap-related macros are already defined in mm/internal.h, so I'm planning to place the code right after them for better grouping. Does that work for you? ``` ... #define MEMCG_RECLAIM_MAY_SWAP (1 << 1) #define MEMCG_RECLAIM_PROACTIVE (1 << 2) #define MIN_SWAPPINESS 0 #define MAX_SWAPPINESS 200 /* Just reclaim from anon folios in proactive memory reclaim */ #define SWAPPINESS_ANON_ONLY (MAX_SWAPPINESS + 1) extern int vm_swappiness; static inline int mem_cgroup_swappiness(struct mem_cgroup *memcg) { #ifdef CONFIG_MEMCG_V1 /* Cgroup2 doesn't have per-cgroup swappiness */ if (cgroup_subsys_on_dfl(memory_cgrp_subsys)) return READ_ONCE(vm_swappiness); /* root ? */ if (mem_cgroup_disabled() || mem_cgroup_is_root(memcg)) return READ_ONCE(vm_swappiness); return READ_ONCE(memcg->swappiness); #else return READ_ONCE(vm_swappiness); #endif } ... ``` -- Best regards Ridong