From: Catalin Marinas <catalin.marinas@arm.com>
To: Baoquan He <bhe@redhat.com>
Cc: linux-kernel@vger.kernel.org, kexec@lists.infradead.org,
linux-arm-kernel@lists.infradead.org, horms@kernel.org,
thunder.leizhen@huawei.com, John.p.donnelly@oracle.com,
will@kernel.org
Subject: Re: [PATCH v2] arm64: kdump: simplify the reservation behaviour of crashkernel=,high
Date: Fri, 3 Feb 2023 17:50:15 +0000 [thread overview]
Message-ID: <Y91JV7wNu1QQh1Ag@arm.com> (raw)
In-Reply-To: <20230203075723.114538-1-bhe@redhat.com>
On Fri, Feb 03, 2023 at 03:57:23PM +0800, Baoquan He wrote:
> On arm64, reservation for 'crashkernel=xM,high' is taken by searching for
> suitable memory region top down. If the 'xM' of crashkernel high memory
> is reserved from high memory successfully, it will try to reserve
> crashkernel low memory later accoringly. Otherwise, it will try to search
> low memory area for the 'xM' suitable region. Please see the details in
> Documentation/admin-guide/kernel-parameters.txt.
>
> While we observed an unexpected case where a reserved region crosses the
> high and low meomry boundary. E.g on a system with 4G as low memory end,
> user added the kernel parameters like: 'crashkernel=512M,high', it could
> finally have [4G-126M, 4G+386M], [1G, 1G+128M] regions in running kernel.
> The crossing 4G boudary of crashkernel high region will bring issues:
>
> 1) For crashkernel=x,high, if getting crashkernel high region across
> 4G boudary, then user will see two memory regions under 4G, and one
> memory region above 4G. The two crashkernel low memory regions are
> confusing.
Looking at your patch, I just realised that the 4G boundary between
'low' and 'high' reservations is not always true. On RPi4, that would be
1GB, the limit of ZONE_DMA. Are there user-space tools that rely on this
32-bit boundary? If they do, they'd get confused on RPi4, not sure they
have the notion of the actual ZONE_DMA that the kernel has enabled. If
we do want ,high to mean always 4G or higher, we'd need to change the
logic a bit so that the search_base starts from 4G rather than
CRASH_ADDR_LOW_MAX. We could leave the latter when ,high was not
specified.
> 2) If people explicityly specify "crashkernel=x,high crashkernel=y,low"
> and y <= 128M, when crashkernel high region crosses 4G boudary and the
> part below 4G of crashkernel high reservation is bigger than y, the
> expected crahskernel low reservation will be skipped. But the expected
> crashkernel high reservation is shrank and could not satisfy user space
> requirement.
I guess if the user passes both high and low, we should honour that and
ignore any y <= 128M checks.
--
Catalin
_______________________________________________
kexec mailing list
kexec@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/kexec
WARNING: multiple messages have this Message-ID (diff)
From: Catalin Marinas <catalin.marinas@arm.com>
To: Baoquan He <bhe@redhat.com>
Cc: linux-kernel@vger.kernel.org, kexec@lists.infradead.org,
linux-arm-kernel@lists.infradead.org, horms@kernel.org,
thunder.leizhen@huawei.com, John.p.donnelly@oracle.com,
will@kernel.org
Subject: Re: [PATCH v2] arm64: kdump: simplify the reservation behaviour of crashkernel=,high
Date: Fri, 3 Feb 2023 17:50:15 +0000 [thread overview]
Message-ID: <Y91JV7wNu1QQh1Ag@arm.com> (raw)
In-Reply-To: <20230203075723.114538-1-bhe@redhat.com>
On Fri, Feb 03, 2023 at 03:57:23PM +0800, Baoquan He wrote:
> On arm64, reservation for 'crashkernel=xM,high' is taken by searching for
> suitable memory region top down. If the 'xM' of crashkernel high memory
> is reserved from high memory successfully, it will try to reserve
> crashkernel low memory later accoringly. Otherwise, it will try to search
> low memory area for the 'xM' suitable region. Please see the details in
> Documentation/admin-guide/kernel-parameters.txt.
>
> While we observed an unexpected case where a reserved region crosses the
> high and low meomry boundary. E.g on a system with 4G as low memory end,
> user added the kernel parameters like: 'crashkernel=512M,high', it could
> finally have [4G-126M, 4G+386M], [1G, 1G+128M] regions in running kernel.
> The crossing 4G boudary of crashkernel high region will bring issues:
>
> 1) For crashkernel=x,high, if getting crashkernel high region across
> 4G boudary, then user will see two memory regions under 4G, and one
> memory region above 4G. The two crashkernel low memory regions are
> confusing.
Looking at your patch, I just realised that the 4G boundary between
'low' and 'high' reservations is not always true. On RPi4, that would be
1GB, the limit of ZONE_DMA. Are there user-space tools that rely on this
32-bit boundary? If they do, they'd get confused on RPi4, not sure they
have the notion of the actual ZONE_DMA that the kernel has enabled. If
we do want ,high to mean always 4G or higher, we'd need to change the
logic a bit so that the search_base starts from 4G rather than
CRASH_ADDR_LOW_MAX. We could leave the latter when ,high was not
specified.
> 2) If people explicityly specify "crashkernel=x,high crashkernel=y,low"
> and y <= 128M, when crashkernel high region crosses 4G boudary and the
> part below 4G of crashkernel high reservation is bigger than y, the
> expected crahskernel low reservation will be skipped. But the expected
> crashkernel high reservation is shrank and could not satisfy user space
> requirement.
I guess if the user passes both high and low, we should honour that and
ignore any y <= 128M checks.
--
Catalin
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
WARNING: multiple messages have this Message-ID (diff)
From: Catalin Marinas <catalin.marinas@arm.com>
To: Baoquan He <bhe@redhat.com>
Cc: linux-kernel@vger.kernel.org, kexec@lists.infradead.org,
linux-arm-kernel@lists.infradead.org, horms@kernel.org,
thunder.leizhen@huawei.com, John.p.donnelly@oracle.com,
will@kernel.org
Subject: Re: [PATCH v2] arm64: kdump: simplify the reservation behaviour of crashkernel=,high
Date: Fri, 3 Feb 2023 17:50:15 +0000 [thread overview]
Message-ID: <Y91JV7wNu1QQh1Ag@arm.com> (raw)
In-Reply-To: <20230203075723.114538-1-bhe@redhat.com>
On Fri, Feb 03, 2023 at 03:57:23PM +0800, Baoquan He wrote:
> On arm64, reservation for 'crashkernel=xM,high' is taken by searching for
> suitable memory region top down. If the 'xM' of crashkernel high memory
> is reserved from high memory successfully, it will try to reserve
> crashkernel low memory later accoringly. Otherwise, it will try to search
> low memory area for the 'xM' suitable region. Please see the details in
> Documentation/admin-guide/kernel-parameters.txt.
>
> While we observed an unexpected case where a reserved region crosses the
> high and low meomry boundary. E.g on a system with 4G as low memory end,
> user added the kernel parameters like: 'crashkernel=512M,high', it could
> finally have [4G-126M, 4G+386M], [1G, 1G+128M] regions in running kernel.
> The crossing 4G boudary of crashkernel high region will bring issues:
>
> 1) For crashkernel=x,high, if getting crashkernel high region across
> 4G boudary, then user will see two memory regions under 4G, and one
> memory region above 4G. The two crashkernel low memory regions are
> confusing.
Looking at your patch, I just realised that the 4G boundary between
'low' and 'high' reservations is not always true. On RPi4, that would be
1GB, the limit of ZONE_DMA. Are there user-space tools that rely on this
32-bit boundary? If they do, they'd get confused on RPi4, not sure they
have the notion of the actual ZONE_DMA that the kernel has enabled. If
we do want ,high to mean always 4G or higher, we'd need to change the
logic a bit so that the search_base starts from 4G rather than
CRASH_ADDR_LOW_MAX. We could leave the latter when ,high was not
specified.
> 2) If people explicityly specify "crashkernel=x,high crashkernel=y,low"
> and y <= 128M, when crashkernel high region crosses 4G boudary and the
> part below 4G of crashkernel high reservation is bigger than y, the
> expected crahskernel low reservation will be skipped. But the expected
> crashkernel high reservation is shrank and could not satisfy user space
> requirement.
I guess if the user passes both high and low, we should honour that and
ignore any y <= 128M checks.
--
Catalin
next prev parent reply other threads:[~2023-02-03 17:50 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-03 7:57 [PATCH v2] arm64: kdump: simplify the reservation behaviour of crashkernel=,high Baoquan He
2023-02-03 7:57 ` Baoquan He
2023-02-03 7:57 ` Baoquan He
2023-02-03 17:50 ` Catalin Marinas [this message]
2023-02-03 17:50 ` Catalin Marinas
2023-02-03 17:50 ` Catalin Marinas
2023-02-07 3:59 ` Baoquan He
2023-02-07 3:59 ` Baoquan He
2023-02-07 3:59 ` Baoquan He
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=Y91JV7wNu1QQh1Ag@arm.com \
--to=catalin.marinas@arm.com \
--cc=John.p.donnelly@oracle.com \
--cc=bhe@redhat.com \
--cc=horms@kernel.org \
--cc=kexec@lists.infradead.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=thunder.leizhen@huawei.com \
--cc=will@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.