linux-kernel - Re: [PATCH 4/7] node: Add memory caching attributes

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Message-ID: <20181126151446.GK26707@localhost.localdomain>
Date:   Mon, 26 Nov 2018 08:14:47 -0700
From:   Keith Busch <keith.busch@...el.com>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        linux-mm@...ck.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rafael Wysocki <rafael@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH 4/7] node: Add memory caching attributes

On Thu, Nov 22, 2018 at 06:59:21PM +0530, Anshuman Khandual wrote:
> 
> 
> On 11/20/2018 04:36 AM, Keith Busch wrote:
> > On Mon, Nov 19, 2018 at 09:44:00AM +0530, Anshuman Khandual wrote:
> >> On 11/15/2018 04:19 AM, Keith Busch wrote:
> >>> System memory may have side caches to help improve access speed. While
> >>> the system provided cache is transparent to the software accessing
> >>> these memory ranges, applications can optimize their own access based
> >>> on cache attributes.
> >>
> >> Cache is not a separate memory attribute. It impacts how the real attributes
> >> like bandwidth, latency e.g which are already captured in the previous patch.
> >> What is the purpose of adding this as a separate attribute ? Can you explain
> >> how this is going to help the user space apart from the hints it has already
> >> received with bandwidth, latency etc properties.
> > 
> > I am not sure I understand the question here. Access bandwidth and latency
> > are entirely attributes different than what this patch provides. If the
> > system side-caches memory, the associativity, line size, and total size
> > can optionally be used by software to improve performance.
> 
> Okay but then does this belong to this series which about memory attributes ?

This patch series is about exporting memory attributes, and this system
memory caching is  one such attribute, so yes, I think it belongs.