From: Pavel Tatashin <pasha.tatashin@oracle.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: steven.sistare@oracle.com, daniel.m.jordan@oracle.com,
akpm@linux-foundation.org, mgorman@techsingularity.net,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v1 1/1] mm: buddy page accessed before initialized
Date: Thu, 2 Nov 2017 12:10:39 -0400 [thread overview]
Message-ID: <8b3bb799-818b-b6b6-7c6b-9eee709decb7@oracle.com> (raw)
In-Reply-To: <20171102142742.gpkif3hgnd62nyol@dhcp22.suse.cz>
>>
>> Yes, but as I said, unfortunately memset(1) with CONFIG_VM_DEBUG does not
>> catch this case. So, when CONFIG_VM_DEBUG is enabled kexec reboots without
>> issues.
>
> Can we make the init pattern to catch this?
Unfortunately, that is not easy: memset() gives us only one byte to play
with, and if we use something else that will make CONFIG_VM_DEBUG
unacceptably slow.
One byte is not enough to trigger the pattern that satisfy
page_is_buddy() logic. I have tried it. With kexec, however it is more
predictable: we use the same memory during boot to allocate vmemmap, and
therefore the struct pages are more like "valid" struct pages from the
previous boot.
>
>>>>>> This is why we must initialize the computed buddy page beforehand.
>>>>>
>>>>> Ble, this is really ugly. I will think about it more.
>>>>>
>>>>
>>>> Another approach that I considered is to split loop inside
>>>> deferred_init_range() into two loops: one where we initialize pages by
>>>> calling __init_single_page(), another where we free them to buddy allocator
>>>> by calling deferred_free_range().
>>>
>>> Yes, that would make much more sense to me.
>>>
>>
>> Ok, so should I submit a new patch with two loops? (The logic within loops
>> is going to be the same:
>
> Could you post it please?
>
>> if (!pfn_valid_within(pfn)) {
>> } else if (!(pfn & nr_pgmask) && !pfn_valid(pfn)) {
>> } else if (!meminit_pfn_in_nid(pfn, nid, &nid_init_state)) {
>> } else if (page && (pfn & nr_pgmask)) {
>>
>> This fix was already added into mm-tree as
>> mm-deferred_init_memmap-improvements-fix-2.patch
>
> I think Andrew can drop it and replace by a different patch.
>
The new patch is coming, I will test it on two machines where I observed
the problem.
Thank you,
Pasha
next prev parent reply other threads:[~2017-11-02 16:10 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-31 15:50 [PATCH v1 0/1] buddy page accessed before initialized Pavel Tatashin
2017-10-31 15:50 ` [PATCH v1 1/1] mm: " Pavel Tatashin
2017-11-02 13:32 ` Michal Hocko
2017-11-02 13:39 ` Pavel Tatashin
2017-11-02 13:54 ` Michal Hocko
2017-11-02 14:00 ` Pavel Tatashin
2017-11-02 14:08 ` Michal Hocko
2017-11-02 14:16 ` Pavel Tatashin
2017-11-02 14:27 ` Michal Hocko
2017-11-02 16:10 ` Pavel Tatashin [this message]
2017-11-03 8:59 ` Michal Hocko
2017-11-03 14:17 ` Pavel Tatashin
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