From: Michal Hocko <mhocko@kernel.org>
To: Pasha Tatashin <pasha.tatashin@oracle.com>
Cc: linux-kernel@vger.kernel.org, sparclinux@vger.kernel.org,
linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org,
linux-s390@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
x86@kernel.org, kasan-dev@googlegroups.com,
borntraeger@de.ibm.com, heiko.carstens@de.ibm.com,
davem@davemloft.net, willy@infradead.org,
ard.biesheuvel@linaro.org, mark.rutland@arm.com,
will.deacon@arm.com, catalin.marinas@arm.com, sam@ravnborg.org,
mgorman@techsingularity.net, steven.sistare@oracle.com,
daniel.m.jordan@oracle.com, bob.picco@oracle.com
Subject: Re: [PATCH v9 08/12] mm: zero reserved and unavailable struct pages
Date: Wed, 4 Oct 2017 16:04:10 +0200 [thread overview]
Message-ID: <20171004140410.2w2zf2gbutdxunir@dhcp22.suse.cz> (raw)
In-Reply-To: <d743668c-6b7e-1775-a5b8-d6e997537990@oracle.com>
On Wed 04-10-17 09:28:55, Pasha Tatashin wrote:
>
> > I am not really familiar with the trim_low_memory_range code path. I am
> > not even sure we have to care about it because nobody should be walking
> > pfns outside of any zone.
>
> According to commit comments first 4K belongs to BIOS, so I think the memory
> exists but BIOS may or may not report it to Linux. So, reserve it to make
> sure we never touch it.
Yes and that memory should be outside of any zones, no?
> > I am worried that this patch adds a code which
> > is not really used and it will just stay that way for ever because
> > nobody will dare to change it as it is too obscure and not explained
> > very well.
>
> I could explain mine code better. Perhaps add more comments, and explain
> when it can be removed?
More explanation would be definitely helpful
> > trim_low_memory_range is a good example of this. Why do we
> > even reserve this range from the memory block allocator? The memory
> > shouldn't be backed by any real memory and thus not in the allocator in
> > the first place, no?
> >
>
> Since it is not enforced in memblock that everything in reserved list must
> be part of memory list, we can have it, and we need to make sure kernel does
> not panic. Otherwise, it is very hard to detect such bugs.
So, should we report such a memblock reservation API (ab)use to the log?
Are you actually sure that trim_low_memory_range is doing a sane and
really needed thing? In other words do we have a zone which contains
this no-memory backed pfns?
--
Michal Hocko
SUSE Labs
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next prev parent reply other threads:[~2017-10-04 14:04 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-20 20:17 [PATCH v9 00/12] complete deferred page initialization Pavel Tatashin
2017-09-20 20:17 ` [PATCH v9 01/12] x86/mm: setting fields in deferred pages Pavel Tatashin
2017-10-03 12:26 ` Michal Hocko
2017-10-03 15:07 ` Pasha Tatashin
2017-09-20 20:17 ` [PATCH v9 02/12] sparc64/mm: " Pavel Tatashin
2017-10-03 12:28 ` Michal Hocko
2017-10-03 15:10 ` Pasha Tatashin
2017-09-20 20:17 ` [PATCH v9 03/12] mm: deferred_init_memmap improvements Pavel Tatashin
2017-10-03 12:57 ` Michal Hocko
2017-10-03 15:15 ` Pasha Tatashin
2017-10-03 16:01 ` Pasha Tatashin
2017-10-04 8:48 ` Michal Hocko
2017-09-20 20:17 ` [PATCH v9 04/12] sparc64: simplify vmemmap_populate Pavel Tatashin
2017-10-03 12:59 ` Michal Hocko
2017-10-03 15:20 ` Pasha Tatashin
2017-09-20 20:17 ` [PATCH v9 05/12] mm: defining memblock_virt_alloc_try_nid_raw Pavel Tatashin
2017-09-20 20:17 ` [PATCH v9 06/12] mm: zero struct pages during initialization Pavel Tatashin
2017-10-03 13:08 ` Michal Hocko
2017-10-03 15:22 ` Pasha Tatashin
2017-10-04 8:45 ` Michal Hocko
2017-10-04 12:26 ` Pasha Tatashin
2017-09-20 20:17 ` [PATCH v9 07/12] sparc64: optimized struct page zeroing Pavel Tatashin
2017-09-20 20:17 ` [PATCH v9 08/12] mm: zero reserved and unavailable struct pages Pavel Tatashin
2017-10-03 13:18 ` Michal Hocko
2017-10-03 15:29 ` Pasha Tatashin
2017-10-04 8:56 ` Michal Hocko
2017-10-04 12:40 ` Pasha Tatashin
2017-10-04 12:57 ` Michal Hocko
2017-10-04 13:28 ` Pasha Tatashin
2017-10-04 14:04 ` Michal Hocko [this message]
2017-10-04 15:08 ` Pasha Tatashin
2017-09-20 20:17 ` [PATCH v9 09/12] mm/kasan: kasan specific map populate function Pavel Tatashin
2017-10-03 14:48 ` Mark Rutland
2017-10-03 15:04 ` Pasha Tatashin
2017-10-09 17:13 ` Will Deacon
2017-10-09 17:51 ` Pavel Tatashin
2017-10-09 18:14 ` Michal Hocko
2017-10-09 18:48 ` Will Deacon
2017-10-09 18:22 ` Will Deacon
2017-10-09 18:42 ` Pavel Tatashin
2017-10-09 18:48 ` Will Deacon
2017-10-09 18:59 ` Pavel Tatashin
2017-10-09 19:02 ` Will Deacon
2017-10-09 19:07 ` Pavel Tatashin
2017-10-09 19:57 ` Pavel Tatashin
2017-09-20 20:17 ` [PATCH v9 10/12] x86/kasan: use kasan_map_populate() Pavel Tatashin
2017-09-20 20:17 ` [PATCH v9 11/12] arm64/kasan: " Pavel Tatashin
2017-09-20 20:17 ` [PATCH v9 12/12] mm: stop zeroing memory during allocation in vmemmap Pavel Tatashin
2017-10-03 13:19 ` Michal Hocko
2017-10-03 15:34 ` Pasha Tatashin
2017-10-03 20:26 ` Pasha Tatashin
2017-10-04 8:45 ` Michal Hocko
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