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To:     Michal Hocko <mhocko@kernel.org>
Cc:     "Michael S. Tsirkin" <mst@redhat.com>,
        Alexander Duyck <alexander.h.duyck@linux.intel.com>,
        Alexander Duyck <alexander.duyck@gmail.com>,
        virtio-dev@lists.oasis-open.org, kvm list <kvm@vger.kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Dave Hansen <dave.hansen@intel.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Matthew Wilcox <willy@infradead.org>,
        linux-mm <linux-mm@kvack.org>,
        Andrew Morton <akpm@linux-foundation.org>, will@kernel.org,
        linux-arm-kernel@lists.infradead.org,
        Oscar Salvador <osalvador@suse.de>,
        Yang Zhang <yang.zhang.wz@gmail.com>,
        Pankaj Gupta <pagupta@redhat.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        Nitesh Narayan Lal <nitesh@redhat.com>,
        Rik van Riel <riel@surriel.com>, lcapitulino@redhat.com,
        "Wang, Wei W" <wei.w.wang@intel.com>,
        Andrea Arcangeli <aarcange@redhat.com>, ying.huang@intel.com,
        Paolo Bonzini <pbonzini@redhat.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Fengguang Wu <fengguang.wu@intel.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
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From:   David Hildenbrand <david@redhat.com>
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Message-ID: <abea20a0-463c-68c0-e810-2e341d971b30@redhat.com>
Date:   Wed, 11 Sep 2019 18:09:18 +0200
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On 11.09.19 15:51, Michal Hocko wrote:
> On Wed 11-09-19 15:20:02, Michal Hocko wrote:
> [...]
>>> 4. Continuously report, not the "one time report everything" approach.
>>
>> So you mean the allocator reporting this rather than an external code to
>> poll right? I do not know, how much this is nice to have than must have?
> 
> Another idea that I haven't really thought through so it might turned
> out to be completely bogus but let's try anyway. Your "report everything"
> just made me look and realize that free_pages_prepare already performs
> stuff that actually does something similar yet unrelated.
> 
> We do report to special page poisoning, zeroying or
> CONFIG_DEBUG_PAGEALLOC to unmap the address from the kernel address
> space. This sounds like something fitting your model no?
> 

AFAIKS, the poisoning/unmapping is done whenever a page is freed. I
don't quite see yet how that would help to remember if a page was
already reported. After reporting the page we would have to switch some
state (Nitesh: bitmap bit, Alexander: page flag) to identify that.

Of course, we could map the page and treat that as "the state" when we
reported it, but I am not sure that's such a good idea :)

As always, I might be very wrong ...

-- 

Thanks,

David / dhildenb