From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>,
linux-doc@vger.kernel.org, Hugh Dickins <hughd@google.com>,
kexec@lists.infradead.org, linux-kernel@vger.kernel.org,
Ingo Molnar <mingo@kernel.org>,
Christoph Hellwig <hch@infradead.org>,
linux-mm@kvack.org, Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Andrew Morton <akpm@linux-foundation.org>,
Vlastimil Babka <vbabka@suse.cz>
Subject: Re: [PATCH] Revert "mm: rename _count, field of the struct page, to _refcount"
Date: Thu, 16 Jun 2016 13:22:27 +0200 [thread overview]
Message-ID: <87a8ilfkek.fsf@vitty.brq.redhat.com> (raw)
In-Reply-To: <20160616105928.GA12437@dhcp22.suse.cz> (Michal Hocko's message of "Thu, 16 Jun 2016 12:59:28 +0200")
Michal Hocko <mhocko@kernel.org> writes:
> On Thu 16-06-16 12:30:16, Vitaly Kuznetsov wrote:
>> Christoph Hellwig <hch@infradead.org> writes:
>>
>> > On Thu, Jun 16, 2016 at 11:22:46AM +0200, Vitaly Kuznetsov wrote:
>> >> _count -> _refcount rename in commit 0139aa7b7fa12 ("mm: rename _count,
>> >> field of the struct page, to _refcount") broke kdump. makedumpfile(8) does
>> >> stuff like READ_MEMBER_OFFSET("page._count", page._count) and fails. While
>> >> it is definitely possible to fix this particular tool I'm not sure about
>> >> other tools which might be doing the same.
>> >>
>> >> I suggest we remember the "we don't break userspace" rule and revert for
>> >> 4.7 while it's not too late.
>> >
>> > Err, sorry - this is not "userspace". It's crazy crap digging into
>> > kernel internal structure.
>> >
>> > The rename was absolutely useful, so fix up your stinking pike in kdump.
>>
>> Ok, sure, I'll send a patch to it. I was worried about other tools out
>> there which e.g. inspect /proc/vmcore. As it is something we support
>> some conservatism around it is justified.
>
> struct page layout as some others that such a tool might depend on has
> changes several times in the past so I fail to see how is it any
> different this time.
IMO this time the change doesn't give us any advantage, it was just a
rename.
> struct page is nothing the userspace should depend on.
True but at least makedumpfile(8) is special and even if it's a 'crazy
crap digging into ...' we could avoid breaking it for no technical
reason.
--
Vitaly
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kexec@lists.infradead.org
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WARNING: multiple messages have this Message-ID (diff)
From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: Christoph Hellwig <hch@infradead.org>,
linux-mm@kvack.org, kexec@lists.infradead.org,
linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Andrew Morton <akpm@linux-foundation.org>,
Stephen Rothwell <sfr@canb.auug.org.au>,
Vlastimil Babka <vbabka@suse.cz>, Hugh Dickins <hughd@google.com>,
Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH] Revert "mm: rename _count, field of the struct page, to _refcount"
Date: Thu, 16 Jun 2016 13:22:27 +0200 [thread overview]
Message-ID: <87a8ilfkek.fsf@vitty.brq.redhat.com> (raw)
In-Reply-To: <20160616105928.GA12437@dhcp22.suse.cz> (Michal Hocko's message of "Thu, 16 Jun 2016 12:59:28 +0200")
Michal Hocko <mhocko@kernel.org> writes:
> On Thu 16-06-16 12:30:16, Vitaly Kuznetsov wrote:
>> Christoph Hellwig <hch@infradead.org> writes:
>>
>> > On Thu, Jun 16, 2016 at 11:22:46AM +0200, Vitaly Kuznetsov wrote:
>> >> _count -> _refcount rename in commit 0139aa7b7fa12 ("mm: rename _count,
>> >> field of the struct page, to _refcount") broke kdump. makedumpfile(8) does
>> >> stuff like READ_MEMBER_OFFSET("page._count", page._count) and fails. While
>> >> it is definitely possible to fix this particular tool I'm not sure about
>> >> other tools which might be doing the same.
>> >>
>> >> I suggest we remember the "we don't break userspace" rule and revert for
>> >> 4.7 while it's not too late.
>> >
>> > Err, sorry - this is not "userspace". It's crazy crap digging into
>> > kernel internal structure.
>> >
>> > The rename was absolutely useful, so fix up your stinking pike in kdump.
>>
>> Ok, sure, I'll send a patch to it. I was worried about other tools out
>> there which e.g. inspect /proc/vmcore. As it is something we support
>> some conservatism around it is justified.
>
> struct page layout as some others that such a tool might depend on has
> changes several times in the past so I fail to see how is it any
> different this time.
IMO this time the change doesn't give us any advantage, it was just a
rename.
> struct page is nothing the userspace should depend on.
True but at least makedumpfile(8) is special and even if it's a 'crazy
crap digging into ...' we could avoid breaking it for no technical
reason.
--
Vitaly
--
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WARNING: multiple messages have this Message-ID (diff)
From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: Christoph Hellwig <hch@infradead.org>,
linux-mm@kvack.org, kexec@lists.infradead.org,
linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Andrew Morton <akpm@linux-foundation.org>,
Stephen Rothwell <sfr@canb.auug.org.au>,
Vlastimil Babka <vbabka@suse.cz>, Hugh Dickins <hughd@google.com>,
Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH] Revert "mm: rename _count, field of the struct page, to _refcount"
Date: Thu, 16 Jun 2016 13:22:27 +0200 [thread overview]
Message-ID: <87a8ilfkek.fsf@vitty.brq.redhat.com> (raw)
In-Reply-To: <20160616105928.GA12437@dhcp22.suse.cz> (Michal Hocko's message of "Thu, 16 Jun 2016 12:59:28 +0200")
Michal Hocko <mhocko@kernel.org> writes:
> On Thu 16-06-16 12:30:16, Vitaly Kuznetsov wrote:
>> Christoph Hellwig <hch@infradead.org> writes:
>>
>> > On Thu, Jun 16, 2016 at 11:22:46AM +0200, Vitaly Kuznetsov wrote:
>> >> _count -> _refcount rename in commit 0139aa7b7fa12 ("mm: rename _count,
>> >> field of the struct page, to _refcount") broke kdump. makedumpfile(8) does
>> >> stuff like READ_MEMBER_OFFSET("page._count", page._count) and fails. While
>> >> it is definitely possible to fix this particular tool I'm not sure about
>> >> other tools which might be doing the same.
>> >>
>> >> I suggest we remember the "we don't break userspace" rule and revert for
>> >> 4.7 while it's not too late.
>> >
>> > Err, sorry - this is not "userspace". It's crazy crap digging into
>> > kernel internal structure.
>> >
>> > The rename was absolutely useful, so fix up your stinking pike in kdump.
>>
>> Ok, sure, I'll send a patch to it. I was worried about other tools out
>> there which e.g. inspect /proc/vmcore. As it is something we support
>> some conservatism around it is justified.
>
> struct page layout as some others that such a tool might depend on has
> changes several times in the past so I fail to see how is it any
> different this time.
IMO this time the change doesn't give us any advantage, it was just a
rename.
> struct page is nothing the userspace should depend on.
True but at least makedumpfile(8) is special and even if it's a 'crazy
crap digging into ...' we could avoid breaking it for no technical
reason.
--
Vitaly
next prev parent reply other threads:[~2016-06-16 11:22 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-16 9:22 [PATCH] Revert "mm: rename _count, field of the struct page, to _refcount" Vitaly Kuznetsov
2016-06-16 9:22 ` Vitaly Kuznetsov
2016-06-16 9:22 ` Vitaly Kuznetsov
2016-06-16 9:32 ` Christoph Hellwig
2016-06-16 9:32 ` Christoph Hellwig
2016-06-16 9:32 ` Christoph Hellwig
2016-06-16 10:30 ` Vitaly Kuznetsov
2016-06-16 10:30 ` Vitaly Kuznetsov
2016-06-16 10:30 ` Vitaly Kuznetsov
2016-06-16 10:59 ` Michal Hocko
2016-06-16 10:59 ` Michal Hocko
2016-06-16 10:59 ` Michal Hocko
2016-06-16 11:22 ` Vitaly Kuznetsov [this message]
2016-06-16 11:22 ` Vitaly Kuznetsov
2016-06-16 11:22 ` Vitaly Kuznetsov
2016-06-16 11:28 ` Michal Hocko
2016-06-16 11:28 ` Michal Hocko
2016-06-16 11:28 ` Michal Hocko
2016-06-16 9:36 ` Vlastimil Babka
2016-06-16 9:36 ` Vlastimil Babka
2016-06-16 9:36 ` Vlastimil Babka
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