linux-kernel - Re: [PATCH v1 04/11] fs/proc/vmcore: move vmcore definitions from kcore.h to crash

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Message-ID: <Zz64efFyFstyDdN8@MiWiFi-R3L-srv>
Date: Thu, 21 Nov 2024 12:35:05 +0800
From: Baoquan He <bhe@...hat.com>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-s390@...r.kernel.org, virtualization@...ts.linux.dev,
	kvm@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	kexec@...ts.infradead.org, Heiko Carstens <hca@...ux.ibm.com>,
	Vasily Gorbik <gor@...ux.ibm.com>,
	Alexander Gordeev <agordeev@...ux.ibm.com>,
	Christian Borntraeger <borntraeger@...ux.ibm.com>,
	Sven Schnelle <svens@...ux.ibm.com>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Jason Wang <jasowang@...hat.com>,
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
	Eugenio Pérez <eperezma@...hat.com>,
	Vivek Goyal <vgoyal@...hat.com>, Dave Young <dyoung@...hat.com>,
	Thomas Huth <thuth@...hat.com>, Cornelia Huck <cohuck@...hat.com>,
	Janosch Frank <frankja@...ux.ibm.com>,
	Claudio Imbrenda <imbrenda@...ux.ibm.com>,
	Eric Farman <farman@...ux.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v1 04/11] fs/proc/vmcore: move vmcore definitions from
 kcore.h to crash_dump.h

On 11/20/24 at 11:28am, David Hildenbrand wrote:
> On 20.11.24 10:42, Baoquan He wrote:
> > On 11/15/24 at 10:59am, David Hildenbrand wrote:
> > > On 15.11.24 10:44, Baoquan He wrote:
> > > > On 10/25/24 at 05:11pm, David Hildenbrand wrote:
> > > > > These defines are not related to /proc/kcore, move them to crash_dump.h
> > > > > instead. While at it, rename "struct vmcore" to "struct
> > > > > vmcore_mem_node", which is a more fitting name.
> > > > 
> > > > Agree it's inappropriate to put the defintions in kcore.h. However for
> > > > 'struct vmcore', it's only used in fs/proc/vmcore.c from my code
> > > > serching, do you think if we can put it in fs/proc/vmcore.c directly?
> > > > And 'struct vmcoredd_node' too.
> > > 
> > > See the next patches and how virtio-mem will make use of the feactored out
> > > functions. Not putting them as inline functions into a header will require
> > > exporting symbols just do add a vmcore memory node to the list, which I want
> > > to avoid -- overkill for these simple helpers.
> > 
> > I see. It makes sense to put them in crash_dump.h. Thanks for
> > explanation.
> > 
> 
> I'll add these details to the description.

Thanks.

> 
> > > 
> > > > 
> > > > And about the renaming, with my understanding each instance of struct
> > > > vmcore represents one memory region, isn't it a little confusing to be
> > > > called vmcore_mem_node? I understand you probablly want to unify the
> > > > vmcore and vmcoredd's naming. I have to admit I don't know vmcoredd well
> > > > and its naming, while most of people have been knowing vmcore representing
> > > > memory region very well.
> > > 
> > > I chose "vmcore_mem_node" because it is a memory range stored in a list.
> > > Note the symmetry with "vmcoredd_node"
> > 
> > I would say the justification of naming "vmcore_mem_node" is to keep
> > symmetry with "vmcoredd_node". If because it is a memory range, it really
> > should not be called vmcore_mem_node. As we know, memory node has
> > specific meaning in kernel, it's the memory range existing on a NUMA node.
> > 
> > And vmcoredd is not a widely used feature. At least in fedora/RHEL, we
> > leave it to customers themselves to use and handle, we don't support it.
> > And we add 'novmcoredd' to kdump kernel cmdline by default to disable it
> > in fedora/RHEL. So a rarely used feature should not be taken to decide
> > the naming of a mature and and widely used feature's name. My personal
> > opinion.
> 
> It's a memory range that gets added to a list. So it's a node in a list ...
> representing a memory range. :) I don't particularly care about the "node"
> part here.

Ah, I missed that about list node. There are list items, list entries
and list nodes, I didn't think of list node at tht time.

> 
> The old "struct vmcore" name is misleading: makes one believe it somehow
> represents "/proc/vmcore", but it really doesn't. (see below on function
> naming)

Yeah, agree. struct vmcore is a concept of the whole logical file.

> 
> > 
> > > 
> > > If there are strong feelings I can use a different name, but
> > 
> > Yes, I would suggest we better keep the old name or take a more
> > appropriate one if have to change.
> 
> In light of patch #5 and #6, really only something like "vmcore_mem_node"
> makes sense. Alternatively "vmcore_range" or "vmcore_mem_range".
> 
> Leaving it as "struct vmcore" would mean that we had to do in #5 and #6:
> 
> * vmcore_alloc_add_mem_node() -> vmcore_alloc_add()
> * vmcore_free_mem_nodes() -> vmcore_free()
> 
> Which would *really* be misleading, because we are not "freeing" the vmcore.
> 
> Would "vmcore_range" work for you? Then we could do:
> 
> * vmcore_alloc_add_mem_node() -> vmcore_alloc_add_range()
> * vmcore_free_mem_nodes() -> vmcore_free_ranges()

Yeah, vmcore_range is better, which won't cause misunderstanding.
Thanks.