From: David Hildenbrand <david@redhat.com>
To: Dave Young <dyoung@redhat.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
linux-doc@vger.kernel.org, devel@linuxdriverproject.org,
linux-fsdevel@vger.kernel.org, linux-pm@vger.kernel.org,
xen-devel@lists.xenproject.org,
kexec-ml <kexec@lists.infradead.org>,
pv-drivers@vmware.com, Andrew Morton <akpm@linux-foundation.org>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Baoquan He <bhe@redhat.com>, Omar Sandoval <osandov@fb.com>,
Arnd Bergmann <arnd@arndb.de>,
Matthew Wilcox <willy@infradead.org>,
Michal Hocko <mhocko@suse.com>,
"Michael S. Tsirkin" <mst@redhat.com>,
Lianbo Jiang <lijiang@redhat.com>, Borislav Petkov <bp@alien8.de>,
Kazuhito Hagio <k-hagio@ab.jp.nec.com>
Subject: Re: [PATCH v2 3/8] kexec: export PG_offline to VMCOREINFO
Date: Mon, 11 Mar 2019 10:55:41 +0100 [thread overview]
Message-ID: <d9e578c3-5ae6-5e82-a0a8-14c7e12c729f@redhat.com> (raw)
In-Reply-To: <20190311090402.GA12071@dhcp-128-65.nay.redhat.com>
On 11.03.19 10:04, Dave Young wrote:
> Hi David,
> On 11/22/18 at 11:06am, David Hildenbrand wrote:
>> Right now, pages inflated as part of a balloon driver will be dumped
>> by dump tools like makedumpfile. While XEN is able to check in the
>> crash kernel whether a certain pfn is actuall backed by memory in the
>> hypervisor (see xen_oldmem_pfn_is_ram) and optimize this case, dumps of
>> other balloon inflated memory will essentially result in zero pages getting
>> allocated by the hypervisor and the dump getting filled with this data.
>>
>> The allocation and reading of zero pages can directly be avoided if a
>> dumping tool could know which pages only contain stale information not to
>> be dumped.
>>
>> We now have PG_offline which can be (and already is by virtio-balloon)
>> used for marking pages as logically offline. Follow up patches will
>> make use of this flag also in other balloon implementations.
>>
>> Let's export PG_offline via PAGE_OFFLINE_MAPCOUNT_VALUE, so
>> makedumpfile can directly skip pages that are logically offline and the
>> content therefore stale. (we export is as a macro to match how it is
>> done for PG_buddy. This way it is clearer that this is not actually a flag
>> but only a very specific mapcount value to represent page types).
>>
>> Please note that this is also helpful for a problem we were seeing under
>> Hyper-V: Dumping logically offline memory (pages kept fake offline while
>> onlining a section via online_page_callback) would under some condicions
>> result in a kernel panic when dumping them.
>>
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> Cc: Dave Young <dyoung@redhat.com>
>> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
>> Cc: Baoquan He <bhe@redhat.com>
>> Cc: Omar Sandoval <osandov@fb.com>
>> Cc: Arnd Bergmann <arnd@arndb.de>
>> Cc: Matthew Wilcox <willy@infradead.org>
>> Cc: Michal Hocko <mhocko@suse.com>
>> Cc: "Michael S. Tsirkin" <mst@redhat.com>
>> Cc: Lianbo Jiang <lijiang@redhat.com>
>> Cc: Borislav Petkov <bp@alien8.de>
>> Cc: Kazuhito Hagio <k-hagio@ab.jp.nec.com>
>> Acked-by: Michael S. Tsirkin <mst@redhat.com>
>> Acked-by: Dave Young <dyoung@redhat.com>
>> Signed-off-by: David Hildenbrand <david@redhat.com>
>> ---
>> kernel/crash_core.c | 2 ++
>> 1 file changed, 2 insertions(+)
>>
>> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
>> index 933cb3e45b98..093c9f917ed0 100644
>> --- a/kernel/crash_core.c
>> +++ b/kernel/crash_core.c
>> @@ -464,6 +464,8 @@ static int __init crash_save_vmcoreinfo_init(void)
>> VMCOREINFO_NUMBER(PAGE_BUDDY_MAPCOUNT_VALUE);
>> #ifdef CONFIG_HUGETLB_PAGE
>> VMCOREINFO_NUMBER(HUGETLB_PAGE_DTOR);
>> +#define PAGE_OFFLINE_MAPCOUNT_VALUE (~PG_offline)
>> + VMCOREINFO_NUMBER(PAGE_OFFLINE_MAPCOUNT_VALUE);
>> #endif
>>
>> arch_crash_save_vmcoreinfo();
>
> The patch has been merged, would you mind to send a documentation patch
> for the vmcoreinfo, which is added recently in Documentation/kdump/vmcoreinfo.txt
>
> A brief description about how this vmcoreinfo field is used is good to
> have.
>
Turns out, it was already documented
PG_lru|PG_private|PG_swapcache|PG_swapbacked|PG_slab|PG_hwpoision
|PG_head_mask|PAGE_BUDDY_MAPCOUNT_VALUE(~PG_buddy)
|PAGE_OFFLINE_MAPCOUNT_VALUE(~PG_offline)
-----------------------------------------------------------------
Page attributes. These flags are used to filter various unnecessary for
dumping pages.
Thanks!
> Thanks
> Dave
>
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2019-03-11 9:55 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20181122100627.5189-1-david@redhat.com>
2018-11-22 10:06 ` [PATCH v2 1/8] mm: balloon: update comment about isolation/migration/compaction David Hildenbrand
2018-11-22 10:06 ` [PATCH v2 2/8] mm: convert PG_balloon to PG_offline David Hildenbrand
2018-11-22 10:06 ` [PATCH v2 3/8] kexec: export PG_offline to VMCOREINFO David Hildenbrand
2019-03-11 9:04 ` Dave Young
2019-03-11 9:55 ` David Hildenbrand [this message]
2019-03-11 10:04 ` Dave Young
2018-11-22 10:06 ` [PATCH v2 4/8] xen/balloon: mark inflated pages PG_offline David Hildenbrand
2018-11-23 13:41 ` Juergen Gross
2018-11-22 10:06 ` [PATCH v2 5/8] hv_balloon: " David Hildenbrand
2018-11-22 10:06 ` [PATCH v2 6/8] vmw_balloon: " David Hildenbrand
2018-11-22 10:06 ` [PATCH v2 7/8] PM / Hibernate: use pfn_to_online_page() David Hildenbrand
2018-11-22 10:06 ` [PATCH v2 8/8] PM / Hibernate: exclude all PageOffline() pages David Hildenbrand
2018-11-22 10:09 ` [PATCH v2] makedumpfile: exclude pages that are logically offline David Hildenbrand
2018-11-27 16:32 ` Kazuhito Hagio
2019-03-07 8:41 ` David Hildenbrand
2019-03-11 16:40 ` Kazuhito Hagio
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