From: Pasha Tatashin <pasha.tatashin@oracle.com>
To: Michal Hocko <mhocko@kernel.org>
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 08:40:11 -0400 [thread overview]
Message-ID: <9198a33d-cd40-dd70-4823-7f70c57ef9a2@oracle.com> (raw)
In-Reply-To: <20171004085636.w2rnwf5xxhahzuy7@dhcp22.suse.cz>
>>> Could you be more specific where is such a memory reserved?
>>>
>>
>> I know of one example: trim_low_memory_range() unconditionally reserves from
>> pfn 0, but e820__memblock_setup() might provide the exiting memory from pfn
>> 1 (i.e. KVM).
>
> Then just initialize struct pages for that mapping rigth there where a
> special API is used.
>
>> But, there could be more based on this comment from linux/page-flags.h:
>>
>> 19 * PG_reserved is set for special pages, which can never be swapped out.
>> Some
>> 20 * of them might not even exist (eg empty_bad_page)...
>
> I have no idea wht empty_bad_page is but a quick grep shows that this is
> never used. I might be wrong here but if somebody is reserving a memory
> in a special way then we should handle the initialization right there.
> E.g. create an API for special memblock reservations.
>
Hi Michal,
The reservations happen before struct pages are allocated and mapped.
So, it is not always possible to do it at call sites.
Previously, I have solved this problem like this:
https://patchwork.kernel.org/patch/9886163
But, I was not too happy with that approach, so I replaced it with the
current approach as it is more generic, and solves similar issues if
they happen in other places. Also, the comment in page-flags got me
scared that there are probably other places perhaps on other
architectures that can have the similar issue.
In addition, I did not like my solution, I was simply shrinking the low
reservation from:
[0 - reserve_low) to [min_pfn - reserve_low), but if min_pfn >
reserve_low can we skip low reservation entirely? I was not sure.
The current approach notifies us if there are such pages, and we can
fix/remove them in the future without crashing kernel in the meantime.
Pasha
next prev parent reply other threads:[~2017-10-04 12:41 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 [this message]
2017-10-04 12:57 ` Michal Hocko
2017-10-04 13:28 ` Pasha Tatashin
2017-10-04 14:04 ` Michal Hocko
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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