From: Joonsoo Kim <js1304@gmail.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Linux Memory Management List <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>,
Vlastimil Babka <vbabka@suse.cz>,
Laura Abbott <labbott@redhat.com>,
"Aneesh Kumar K . V" <aneesh.kumar@linux.ibm.com>,
Mel Gorman <mgorman@techsingularity.net>,
Michal Hocko <mhocko@suse.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Roman Gushchin <guro@fb.com>, Minchan Kim <minchan@kernel.org>,
Rik van Riel <riel@surriel.com>,
Christian Koenig <christian.koenig@amd.com>,
Huang Rui <ray.huang@amd.com>,
"Rafael J . Wysocki" <rjw@rjwysocki.net>,
Pavel Machek <pavel@ucw.cz>,
kernel-team@lge.com, Christoph Hellwig <hch@infradead.org>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>
Subject: Re: [PATCH v2 03/10] kexec: separate PageHighMem() and PageHighMemZone() use case
Date: Mon, 4 May 2020 12:10:36 +0900 [thread overview]
Message-ID: <CAAmzW4MrD75+Prw=fQ=d5uXKgGy3urBwmxnNtoNsw5M1m9xjYQ@mail.gmail.com> (raw)
In-Reply-To: <87h7wzvjko.fsf@x220.int.ebiederm.org>
2020년 5월 1일 (금) 오후 11:06, Eric W. Biederman <ebiederm@xmission.com>님이 작성:
>
> js1304@gmail.com writes:
>
> > From: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> >
> > Until now, PageHighMem() is used for two different cases. One is to check
> > if there is a direct mapping for this page or not. The other is to check
> > the zone of this page, that is, weather it is the highmem type zone or not.
> >
> > Now, we have separate functions, PageHighMem() and PageHighMemZone() for
> > each cases. Use appropriate one.
> >
> > Note that there are some rules to determine the proper macro.
> >
> > 1. If PageHighMem() is called for checking if the direct mapping exists
> > or not, use PageHighMem().
> > 2. If PageHighMem() is used to predict the previous gfp_flags for
> > this page, use PageHighMemZone(). The zone of the page is related to
> > the gfp_flags.
> > 3. If purpose of calling PageHighMem() is to count highmem page and
> > to interact with the system by using this count, use PageHighMemZone().
> > This counter is usually used to calculate the available memory for an
> > kernel allocation and pages on the highmem zone cannot be available
> > for an kernel allocation.
> > 4. Otherwise, use PageHighMemZone(). It's safe since it's implementation
> > is just copy of the previous PageHighMem() implementation and won't
> > be changed.
> >
> > I apply the rule #2 for this patch.
>
> Hmm.
>
> What happened to the notion of deprecating and reducing the usage of
> highmem? I know that we have some embedded architectures where it is
> still important but this feels like it flies in the face of that.
AFAIK, deprecating highmem requires some more time and, before then,
we need to support it.
>
> This part of kexec would be much more maintainable if it had a proper
> mm layer helper that tested to see if the page matched the passed in
> gfp flags. That way the mm layer could keep changing and doing weird
> gyrations and this code would not care.
Good idea! I will do it.
>
> What would be really helpful is if there was a straight forward way to
> allocate memory whose physical address fits in the native word size.
>
>
> All I know for certain about this patch is that it takes a piece of code
> that looked like it made sense, and transfroms it into something I can
> not easily verify, and can not maintain.
Although I decide to make a helper as you described above, I don't
understand why you think that a new code isn't maintainable. It is just
the same thing with different name. Could you elaborate more why do
you think so?
Thanks.
next prev parent reply other threads:[~2020-05-04 3:10 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-29 3:26 [PATCH v2 00/10] change the implementation of the PageHighMem() js1304
2020-04-29 3:26 ` [PATCH v2 01/10] mm/page-flags: introduce PageHighMemZone() js1304
2020-04-29 3:26 ` [PATCH v2 02/10] drm/ttm: separate PageHighMem() and PageHighMemZone() use case js1304
2020-04-29 3:26 ` [PATCH v2 03/10] kexec: " js1304
2020-05-01 14:03 ` Eric W. Biederman
2020-05-04 3:10 ` Joonsoo Kim [this message]
2020-05-04 14:03 ` Eric W. Biederman
2020-05-04 21:59 ` [RFC][PATCH] kexec: Teach indirect pages how to live in high memory Eric W. Biederman
2020-05-05 17:44 ` Hari Bathini
2020-05-05 18:39 ` Eric W. Biederman
2020-10-09 1:35 ` Joonsoo Kim
2020-05-06 5:23 ` [PATCH v2 03/10] kexec: separate PageHighMem() and PageHighMemZone() use case Joonsoo Kim
2020-04-29 3:26 ` [PATCH v2 04/10] power: " js1304
2020-05-01 12:22 ` Christoph Hellwig
2020-05-04 3:01 ` Joonsoo Kim
2020-04-29 3:26 ` [PATCH v2 05/10] mm/gup: " js1304
2020-05-01 12:24 ` Christoph Hellwig
2020-05-04 3:02 ` Joonsoo Kim
2020-04-29 3:26 ` [PATCH v2 06/10] mm/hugetlb: " js1304
2020-05-01 12:26 ` Christoph Hellwig
2020-05-04 3:03 ` Joonsoo Kim
2020-04-29 3:26 ` [PATCH v2 07/10] mm: " js1304
2020-05-01 12:30 ` Christoph Hellwig
2020-05-04 3:08 ` Joonsoo Kim
2020-04-29 3:26 ` [PATCH v2 08/10] mm/page_alloc: correct the use of is_highmem_idx() js1304
2020-04-29 3:26 ` [PATCH v2 09/10] mm/migrate: replace PageHighMem() with open-code js1304
2020-04-29 3:26 ` [PATCH v2 10/10] mm/page-flags: change the implementation of the PageHighMem() js1304
2020-04-30 1:47 ` [PATCH v2 00/10] " Andrew Morton
2020-05-01 10:52 ` Joonsoo Kim
2020-05-01 10:55 ` Christoph Hellwig
2020-05-01 12:15 ` Joonsoo Kim
2020-05-01 12:34 ` Christoph Hellwig
2020-05-04 3:09 ` Joonsoo Kim
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