Re: [PATCH] mm: enable page poisoning early at boot

[Vinayak Menon <vinmenon@codeaurora.org>]

On 3/29/2017 10:44 PM, Laura Abbott wrote:
> On 03/29/2017 10:04 AM, Laura Abbott wrote:
>> On 03/24/2017 05:24 AM, Vinayak Menon wrote:
>>> On SPARSEMEM systems page poisoning is enabled after buddy is up, because
>>> of the dependency on page extension init. This causes the pages released
>>> by free_all_bootmem not to be poisoned. This either delays or misses
>>> the identification of some issues because the pages have to undergo another
>>> cycle of alloc-free-alloc for any corruption to be detected.
>>> Enable page poisoning early by getting rid of the PAGE_EXT_DEBUG_POISON
>>> flag. Since all the free pages will now be poisoned, the flag need not be
>>> verified before checking the poison during an alloc.
>>>
>>> Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>
>>> ---
>>>
>>> An RFC was sent earlier (http://www.spinics.net/lists/linux-mm/msg123142.html)
>>> Not sure if there exists a code path that can free pages to buddy skipping
>>> kernel_poison_pages, making the flag PAGE_EXT_DEBUG_POISON a necessity. But
>>> the tests have not shown any issues. As per Laura's suggestion, the patch was
>>> tested with HIBERNATION enabled and no issues were seen.
>>>
>> I gave this a spin on some of my machines and it appears to be working
>> okay. 

Thanks Laura.

>> I wish we had a bit more context about why it was necessary to track
>> the poison in the page itself.
>>
>> This change means that we shouldn't need the "select PAGE_EXTENSION"
>> anymore so that can be dropped. If you do that, you can add
>>
>> Acked-by: Laura Abbott <labbott@redhat.com>
>>
> Actually never mind on dropping the select. It's still needed for
> the guard page as well. Longer term it might be worth separating
> that out as well.

Realized that there is now some redundant CONFIG_PAGE_POISONING checks in page_ext.c. So along
with that I have removed the "select PAGE_EXTENSION"from CONFIG_PAGE_POISONING. Could you
please take a look at v2 ?

>
> You can still take my Ack.
>
> Thanks,
> Laura

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