linux-kernel - Re: [PATCH v6 01/26] fuse: Fix dax truncate/punch

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Message-ID: <CADSE00+2o5Ma0W6FBLHwpUaKut9Tf74GKLCU-377qgxr08EeoQ@mail.gmail.com>
Date: Thu, 6 Feb 2025 15:59:03 +0100
From: Albert Esteve <aesteve@...hat.com>
To: Stefan Hajnoczi <stefanha@...hat.com>
Cc: Vivek Goyal <vgoyal@...hat.com>, Dan Williams <dan.j.williams@...el.com>, 
	Alistair Popple <apopple@...dia.com>, akpm@...ux-foundation.org, linux-mm@...ck.org, 
	alison.schofield@...el.com, lina@...hilina.net, zhang.lyra@...il.com, 
	gerald.schaefer@...ux.ibm.com, vishal.l.verma@...el.com, dave.jiang@...el.com, 
	logang@...tatee.com, bhelgaas@...gle.com, jack@...e.cz, jgg@...pe.ca, 
	catalin.marinas@....com, will@...nel.org, mpe@...erman.id.au, 
	npiggin@...il.com, dave.hansen@...ux.intel.com, ira.weiny@...el.com, 
	willy@...radead.org, djwong@...nel.org, tytso@....edu, linmiaohe@...wei.com, 
	david@...hat.com, peterx@...hat.com, linux-doc@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linuxppc-dev@...ts.ozlabs.org, nvdimm@...ts.linux.dev, 
	linux-cxl@...r.kernel.org, linux-fsdevel@...r.kernel.org, 
	linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org, jhubbard@...dia.com, 
	hch@....de, david@...morbit.com, chenhuacai@...nel.org, kernel@...0n.name, 
	loongarch@...ts.linux.dev, Hanna Czenczek <hreitz@...hat.com>, 
	German Maglione <gmaglione@...hat.com>
Subject: Re: [PATCH v6 01/26] fuse: Fix dax truncate/punch_hole fault path

Hi!

On Thu, Feb 6, 2025 at 3:30 PM Stefan Hajnoczi <stefanha@...hat.com> wrote:
>
> On Thu, Feb 06, 2025 at 08:37:07AM -0500, Vivek Goyal wrote:
> > And then there are challenges at QEMU level. virtiofsd needs additional
> > vhost-user commands to implement DAX and these never went upstream in
> > QEMU. I hope these challenges are sorted at some point of time.
>
> Albert Esteve has been working on QEMU support:
> https://lore.kernel.org/qemu-devel/20240912145335.129447-1-aesteve@redhat.com/
>
> He has a viable solution. I think the remaining issue is how to best
> structure the memory regions. The reason for slow progress is not
> because it can't be done, it's probably just because this is a
> background task.

It is partially that, indeed. But what has me blocked for now on posting the
next version is that I was reworking a bit the MMAP strategy.
Following David comments, I am relying more on RAMBlocks and
subregions for mmaps. But this turned out more difficult than anticipated.

I hope I can make it work this month and then post the next version.
If there are no major blockers/reworks, further iterations on the
patch shall go smoother.

I have a separate patch for the vhost-user spec which could
iterate faster, if that'd help.

BR,
Albert.

>
> Please discuss with Albert if QEMU support is urgent.
>
> Stefan