linux-kernel - Re: [RFC PATCH v3 0/4] Node Weights and Weighted Interleave

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Date:   Mon, 06 Nov 2023 13:08:59 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Gregory Price <gourry.memverge@...il.com>,
        linux-kernel@...r.kernel.org, linux-cxl@...r.kernel.org,
        linux-mm@...ck.org, akpm@...ux-foundation.org,
        aneesh.kumar@...ux.ibm.com, weixugc@...gle.com, apopple@...dia.com,
        tim.c.chen@...el.com, dave.hansen@...el.com, shy828301@...il.com,
        gregkh@...uxfoundation.org, rafael@...nel.org,
        Gregory Price <gregory.price@...verge.com>
Subject: Re: [RFC PATCH v3 0/4] Node Weights and Weighted Interleave

Michal Hocko <mhocko@...e.com> writes:

> On Fri 03-11-23 15:10:37, Huang, Ying wrote:
>> Michal Hocko <mhocko@...e.com> writes:
>> 
>> > On Thu 02-11-23 14:11:09, Huang, Ying wrote:
>> >> Michal Hocko <mhocko@...e.com> writes:
>> >> 
>> >> > On Wed 01-11-23 10:21:47, Huang, Ying wrote:
>> >> >> Michal Hocko <mhocko@...e.com> writes:
>> >> > [...]
>> >> >> > Well, I am not convinced about that TBH. Sure it is probably a good fit
>> >> >> > for this specific CXL usecase but it just doesn't fit into many others I
>> >> >> > can think of - e.g. proportional use of those tiers based on the
>> >> >> > workload - you get what you pay for.
>> >> >> 
>> >> >> For "pay", per my understanding, we need some cgroup based
>> >> >> per-memory-tier (or per-node) usage limit.  The following patchset is
>> >> >> the first step for that.
>> >> >> 
>> >> >> https://lore.kernel.org/linux-mm/cover.1655242024.git.tim.c.chen@linux.intel.com/
>> >> >
>> >> > Why do we need a sysfs interface if there are plans for cgroup API?
>> >> 
>> >> They are for different target.  The cgroup API proposed here is to
>> >> constrain the DRAM usage in a system with DRAM and CXL memory.  The less
>> >> you pay, the less DRAM and more CXL memory you use.
>> >
>> > Right, but why the usage distribution requires its own interface and
>> > cannot be combined with the access control part of it?
>> 
>> Per my understanding, they are orthogonal.
>> 
>> Weighted-interleave is a memory allocation policy, other memory
>> allocation policies include local first, etc.
>> 
>> Usage limit is to constrain the usage of specific memory types
>> (e.g. DRAM) for a cgroup.  It can be used together with local first
>> policy and some other memory allocation policy.
>
> Bad wording from me. Sorry for the confusion.

Never mind.

> Sure those are two orthogonal things and I didn't mean to suggest a
> single API to cover both. But if cgroup semantic can be reasonably
> defined for the usage enforcement can we put the interleaving behavior
> API under the same cgroup controller as well?

I haven't thought about it thoroughly.  But I think it should be the
direction.

--
Best Regards,
Huang, Ying