linux-kernel - Re: [PATCH v12 02/11] mm, swap: Add infrastructure for saving page metadata on swap

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Date:   Mon, 5 Mar 2018 13:04:10 -0800
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Khalid Aziz <khalid.aziz@...cle.com>, akpm@...ux-foundation.org,
        davem@...emloft.net, arnd@...db.de
Cc:     kirill.shutemov@...ux.intel.com, mhocko@...e.com,
        ross.zwisler@...ux.intel.com, dave.jiang@...el.com,
        mgorman@...hsingularity.net, willy@...radead.org, hughd@...gle.com,
        minchan@...nel.org, hannes@...xchg.org, shli@...com,
        mingo@...nel.org, jglisse@...hat.com, me@...in.cc,
        anthony.yznaga@...cle.com, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        sparclinux@...r.kernel.org, Khalid Aziz <khalid@...ehiking.org>
Subject: Re: [PATCH v12 02/11] mm, swap: Add infrastructure for saving page
 metadata on swap

On 03/05/2018 12:28 PM, Khalid Aziz wrote:
>> Do you have a way to tell that data is not being thrown away?  Like if
>> the ADI metadata is different for two different cachelines within a
>> single page?
> 
> Yes, since access to tagged data is made using pointers with ADI tag
> embedded in the top bits, any mismatch between what app thinks the ADI
> tags should be and what is stored in the RAM for corresponding page will
> result in exception. If ADI data gets thrown away, we will get an ADI
> tag mismatch exception. If ADI tags for two different ADI blocks on a
> page are different when app expected them to be the same, we will see an
> exception on access to the block with wrong ADI data.

So, when an app has two different ADI tags on two parts of a page, the
page gets swapped, and the ADI block size is under PAGE_SIZE, the app
will get an ADI exception after swap-in through no fault of its own?