linux-kernel - Re: [RFC PATCH v3] sparc64: Add support for Application Data Integrity (ADI)

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Date:   Fri, 6 Jan 2017 09:22:13 -0700
From:   Khalid Aziz <khalid.aziz@...cle.com>
To:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Michal Hocko <mhocko@...nel.org>
Cc:     Rob Gardner <rob.gardner@...cle.com>, davem@...emloft.net,
        corbet@....net, arnd@...db.de, akpm@...ux-foundation.org,
        hpa@...or.com, viro@...iv.linux.org.uk, nitin.m.gupta@...cle.com,
        chris.hyser@...cle.com, tushar.n.dave@...cle.com,
        sowmini.varadhan@...cle.com, mike.kravetz@...cle.com,
        adam.buchbinder@...il.com, minchan@...nel.org, hughd@...gle.com,
        kirill.shutemov@...ux.intel.com, keescook@...omium.org,
        allen.pais@...cle.com, aryabinin@...tuozzo.com,
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        iamjoonsoo.kim@....com, mgorman@...hsingularity.net,
        vdavydov.dev@...il.com, hannes@...xchg.org, namit@...are.com,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        sparclinux@...r.kernel.org, linux-arch@...r.kernel.org,
        x86@...nel.org, linux-mm@...ck.org,
        Khalid Aziz <khalid@...ehiking.org>
Subject: Re: [RFC PATCH v3] sparc64: Add support for Application Data
 Integrity (ADI)

On 01/06/2017 08:36 AM, Dave Hansen wrote:
> On 01/06/2017 07:32 AM, Khalid Aziz wrote:
>> I agree with you on simplicity first. Subpage granularity is complex,
>> but the architecture allows for subpage granularity. Maybe the right
>> approach is to support this at page granularity first for swappable
>> pages and then expand to subpage granularity in a subsequent patch?
>> Pages locked in memory can already use subpage granularity with my patch.
>
> What do you mean by "locked in memory"?  mlock()'d memory can still be
> migrated around and still requires "swap" ptes, for instance.

You are right. Page migration can invalidate subpage granularity even 
for locked pages. Is it possible to use cpusets to keep a task and its 
memory locked on a single node? Just wondering if there are limited 
cases where subpage granularity could work without supporting subpage 
granularity for tags in swap. It still sounds like the right thing to do 
is to get a reliable implementation in place with page size granularity 
and then add the complexity of subpage granularity.

Thanks,
Khalid