linux-kernel - Re: [PATCH -V6 00/21] swap: Swapout/swapin THP in one piece

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Date:   Wed, 24 Oct 2018 10:24:10 -0700
From:   Daniel Jordan <daniel.m.jordan@...cle.com>
To:     "Huang, Ying" <ying.huang@...el.com>
Cc:     Daniel Jordan <daniel.m.jordan@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Michal Hocko <mhocko@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Shaohua Li <shli@...nel.org>, Hugh Dickins <hughd@...gle.com>,
        Minchan Kim <minchan@...nel.org>,
        Rik van Riel <riel@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Zi Yan <zi.yan@...rutgers.edu>
Subject: Re: [PATCH -V6 00/21] swap: Swapout/swapin THP in one piece

On Wed, Oct 24, 2018 at 11:31:42AM +0800, Huang, Ying wrote:
> Hi, Daniel,
> 
> Daniel Jordan <daniel.m.jordan@...cle.com> writes:
> 
> > On Wed, Oct 10, 2018 at 03:19:03PM +0800, Huang Ying wrote:
> >> And for all, Any comment is welcome!
> >> 
> >> This patchset is based on the 2018-10-3 head of mmotm/master.
> >
> > There seems to be some infrequent memory corruption with THPs that have been
> > swapped out: page contents differ after swapin.
> 
> Thanks a lot for testing this!  I know there were big effort behind this
> and it definitely will improve the quality of the patchset greatly!

You're welcome!  Hopefully I'll have more results and tests to share in the
next two weeks.

> 
> > Reproducer at the bottom.  Part of some tests I'm writing, had to separate it a
> > little hack-ily.  Basically it writes the word offset _at_ each word offset in
> > a memory blob, tries to push it to swap, and verifies the offset is the same
> > after swapin.
> >
> > I ran with THP enabled=always.  THP swapin_enabled could be always or never, it
> > happened with both.  Every time swapping occurred, a single THP-sized chunk in
> > the middle of the blob had different offsets.  Example:
> >
> > ** > word corruption gap
> > ** corruption detected 14929920 bytes in (got 15179776, expected 14929920) **
> > ** corruption detected 14929928 bytes in (got 15179784, expected 14929928) **
> > ** corruption detected 14929936 bytes in (got 15179792, expected 14929936) **
> > ...pattern continues...
> > ** corruption detected 17027048 bytes in (got 15179752, expected 17027048) **
> > ** corruption detected 17027056 bytes in (got 15179760, expected 17027056) **
> > ** corruption detected 17027064 bytes in (got 15179768, expected 17027064) **
> 
> 15179776 < 15179xxx <= 17027064
> 
> 15179776 % 4096 = 0
> 
> And 15179776 = 15179768 + 8
> 
> So I guess we have some alignment bug.  Could you try the patches
> attached?  It deal with some alignment issue.

That fixed it.  And removed three lines of code.  Nice :)