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From: ebiederm@xmission.com (Eric W. Biederman)
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: riel@redhat.com, hughd@google.com, kexec@lists.infradead.org,
	linux-kernel@vger.kernel.org, lisa.mitchell@hp.com,
	linux-mm@kvack.org, HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>,
	kumagai-atsushi@mxc.nes.nec.co.jp, jingbai.ma@hp.com,
	kosaki.motohiro@jp.fujitsu.com, zhangyanfei@cn.fujitsu.com,
	akpm@linux-foundation.org, walken@google.com, cpw@sgi.com,
	vgoyal@redhat.com
Subject: Re: [PATCH v6 0/8] kdump, vmcore: support mmap() on /proc/vmcore
Date: Thu, 16 May 2013 19:53:31 -0700	[thread overview]
Message-ID: <87y5bee2qc.fsf@xmission.com> (raw)
In-Reply-To: <51957469.2000008@zytor.com> (H. Peter Anvin's message of "Thu, 16 May 2013 17:06:01 -0700")

"H. Peter Anvin" <hpa@zytor.com> writes:

> On 05/15/2013 02:05 AM, HATAYAMA Daisuke wrote:
>> Currently, read to /proc/vmcore is done by read_oldmem() that uses
>> ioremap/iounmap per a single page. For example, if memory is 1GB,
>> ioremap/iounmap is called (1GB / 4KB)-times, that is, 262144
>> times. This causes big performance degradation.
>
> read_oldmem() is fundamentally broken and unsafe.  It needs to be
> unified with the plain /dev/mem code and any missing functionality fixed
> instead of "let's just do a whole new driver".

That is completely and totally orthogonal to this change.

read_oldmem may have problems but in practice on a large systems those
problems are totally dwarfed by real life performance issues that come
from playing too much with the page tables.

I really don't find bringing up whatever foundational issues you have
with read_oldmem() appropriate or relevant here.

Eric

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  parent reply	other threads:[~2013-05-17  2:54 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-05-15  9:05 [PATCH v6 0/8] kdump, vmcore: support mmap() on /proc/vmcore HATAYAMA Daisuke
2013-05-15  9:05 ` [PATCH v6 1/8] vmcore: clean up read_vmcore() HATAYAMA Daisuke
2013-05-15  9:33   ` Zhang Yanfei
2013-05-15  9:05 ` [PATCH v6 2/8] vmcore: allocate buffer for ELF headers on page-size alignment HATAYAMA Daisuke
2013-05-16  5:58   ` Zhang Yanfei
2013-05-16 16:51   ` Vivek Goyal
2013-05-17  0:08     ` HATAYAMA Daisuke
2013-05-15  9:05 ` [PATCH v6 3/8] vmcore: treat memory chunks referenced by PT_LOAD program header entries in page-size boundary in vmcore_list HATAYAMA Daisuke
2013-05-16  5:59   ` Zhang Yanfei
2013-05-15  9:06 ` [PATCH v6 4/8] vmalloc: make find_vm_area check in range HATAYAMA Daisuke
2013-05-15 21:37   ` KOSAKI Motohiro
2013-05-16 23:45     ` HATAYAMA Daisuke
2013-05-15  9:06 ` [PATCH v6 5/8] vmalloc: introduce remap_vmalloc_range_partial HATAYAMA Daisuke
2013-05-15  9:06 ` [PATCH v6 6/8] vmcore: allocate ELF note segment in the 2nd kernel vmalloc memory HATAYAMA Daisuke
2013-05-16  7:19   ` Zhang Yanfei
2013-05-16 20:32   ` Vivek Goyal
2013-05-16 23:47     ` HATAYAMA Daisuke
2013-05-15  9:06 ` [PATCH v6 7/8] vmcore: calculate vmcore file size from buffer size and total size of vmcore objects HATAYAMA Daisuke
2013-05-16  7:19   ` Zhang Yanfei
2013-05-15  9:06 ` [PATCH v6 8/8] vmcore: support mmap() on /proc/vmcore HATAYAMA Daisuke
2013-05-16  7:25   ` Zhang Yanfei
2013-05-16 20:44   ` Vivek Goyal
2013-05-17  0:06 ` [PATCH v6 0/8] kdump, " H. Peter Anvin
2013-05-17  1:45   ` HATAYAMA Daisuke
2013-05-17  2:53   ` Eric W. Biederman [this message]
2013-05-17  3:21     ` H. Peter Anvin
2013-05-17  4:29       ` Eric W. Biederman
2013-05-17  5:43         ` H. Peter Anvin

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