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

["Huang\, Ying" <ying.huang@intel.com>]

Hi, Daniel,

Daniel Jordan <daniel.m.jordan@oracle.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!

> 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.

> 100.0% of memory was swapped out at mincore time
> 0.00305% of pages were corrupted (first corrupt word 14929920, last corrupt word 17027064)
>
> The problem goes away with THP enabled=never, and I don't see it on 2018-10-3
> mmotm/master with THP enabled=always.
>
> The server had an NVMe swap device and ~760G memory over two nodes, and the
> program was always run like this:  swap-verify -s $((64 * 2**30))
>
> The kernels had one extra patch, Alexander Duyck's
> "dma-direct: Fix return value of dma_direct_supported", which was required to
> get them to build.
>

Thanks again!

Best Regards,
Huang, Ying

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