linux-kernel - Re: [PATCH 3/5] cifsd: add file operations

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Date:   Mon, 22 Mar 2021 13:02:42 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Sergey Senozhatsky <senozhatsky@...omium.org>
Cc:     Namjae Jeon <namjae.jeon@...sung.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-cifs@...r.kernel.org,
        linux-cifsd-devel@...ts.sourceforge.net,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        linux-mm@...r.kernel.org, Uladzislau Rezki <urezki@...il.com>
Subject: Re: [PATCH 3/5] cifsd: add file operations

On Mon, Mar 22, 2021 at 06:03:21PM +0900, Sergey Senozhatsky wrote:
> On (21/03/22 08:15), Matthew Wilcox wrote:
> > 
> > What's the scenario for which your allocator performs better than slub
> > 
> 
> IIRC request and reply buffers can be up to 4M in size. So this stuff
> just allocates a number of fat buffers and keeps them around so that
> it doesn't have to vmalloc(4M) for every request and every response.

That makes a lot more sense; I was thrown off by the kvmalloc, which
is usually used for allocations that might be smaller than PAGE_SIZE.

So what this patch is really saying is that vmalloc() should include
some caching, so it can defer freeing until there's memory pressure
or it's built up a large (percpu) backlog of freed areas.

Vlad, have you thought about this?