linux-kernel - Re: [PATCH 07/32] mm: Bring back vmalloc

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Date:   Sun, 14 May 2023 23:13:46 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Kent Overstreet <kent.overstreet@...ux.dev>
Cc:     Lorenzo Stoakes <lstoakes@...il.com>,
        Christoph Hellwig <hch@...radead.org>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-bcachefs@...r.kernel.org,
        Kent Overstreet <kent.overstreet@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Uladzislau Rezki <urezki@...il.com>, linux-mm@...ck.org
Subject: Re: [PATCH 07/32] mm: Bring back vmalloc_exec

On Mon, May 15, 2023 at 01:38:51AM -0400, Kent Overstreet wrote:
> On Sun, May 14, 2023 at 11:43:25AM -0700, Eric Biggers wrote:
> > I think it would also help if the generated assembly had the handling of the
> > fields interleaved.  To achieve that, it might be necessary to interleave the C
> > code.
> 
> No, that has negligable effect on performance - as expected, for an out
> of order processor. < 1% improvement.
> 
> It doesn't look like this approach is going to work here. Sadly.

I'd be glad to take a look at the code you actually tried.  It would be helpful
if you actually provided it, instead of just this "I tried it, I'm giving up
now" sort of thing.

I was also hoping you'd take the time to split this out into a userspace
micro-benchmark program that we could quickly try different approaches on.

BTW, even if people are okay with dynamic code generation (which seems
unlikely?), you'll still need a C version for architectures that you haven't
implemented the dynamic code generation for.

- Eric