linux-kernel - Re: [RFC PATCH 0/4] Add fbind() and NUMA mempolicy support for KVM guest

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Message-ID: <ZyzYUOX_r3uWin5f@casper.infradead.org>
Date: Thu, 7 Nov 2024 15:10:08 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Shivank Garg <shivankg@....com>
Cc: x86@...nel.org, viro@...iv.linux.org.uk, brauner@...nel.org,
	jack@...e.cz, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org, linux-api@...r.kernel.org,
	linux-arch@...r.kernel.org, kvm@...r.kernel.org, chao.gao@...el.com,
	pgonda@...gle.com, thomas.lendacky@....com, seanjc@...gle.com,
	luto@...nel.org, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
	dave.hansen@...ux.intel.com, arnd@...db.de, pbonzini@...hat.com,
	kees@...nel.org, bharata@....com, nikunj@....com,
	michael.day@....com, Neeraj.Upadhyay@....com,
	linux-coco@...ts.linux.dev
Subject: Re: [RFC PATCH 0/4] Add fbind() and NUMA mempolicy support for KVM
 guest_memfd

On Thu, Nov 07, 2024 at 02:24:20PM +0530, Shivank Garg wrote:
> The folio allocation path from guest_memfd typically looks like this...
> 
> kvm_gmem_get_folio
>   filemap_grab_folio
>     __filemap_get_folio
>       filemap_alloc_folio
>         __folio_alloc_node_noprof
>           -> goes to the buddy allocator
> 
> Hence, I am trying to have a version of filemap_alloc_folio() that takes an mpol.

It only takes that path if cpuset_do_page_mem_spread() is true.  Is the
real problem that you're trying to solve that cpusets are being used
incorrectly?

Backing up, it seems like you want to make a change to the page cache,
you've had a long discussion with people who aren't the page cache
maintainer, and you all understand the pros and cons of everything,
and here you are dumping a solution on me without talking to me, even
though I was at Plumbers, you didn't find me to tell me I needed to go
to your talk.

So you haven't explained a damned thing to me, and I'm annoyed at you.
Do better.  Starting with your cover letter.