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

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Message-ID: <2i3awgkx2i4a5op7rtcqzv4yub376l66tevfvlyccf6wrjia4v@5x4ar4f6i5eh>
Date:   Fri, 3 Nov 2023 10:39:00 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     "Huang, Ying" <ying.huang@...el.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

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. 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?
-- 
Michal Hocko
SUSE Labs