Re: [PATCH] shrink core hashes on small systems

[Andrew Morton]

Matt Mackall <mpm@xxxxxxxxxxx> wrote:
>
> Shrink hashes on small systems
> 
> Tweak vfs_caches_init logic so that hashes don't start growing as
> quickly on small systems.
> 
> -	vfs_caches_init(num_physpages);
> +	/* Treat machines smaller than 6M as having 2M of memory
> +	   for hash-sizing purposes */
> +	vfs_caches_init(max(500, (int)num_physpages-1000));

This seems rather arbitrary.  It also implicitly "knows" that
PAGE_SIZE=4096.

num_physpages is of course the wrong thing to use here - on small systems
we should be accounting for memory which is pinned by kernel text, etc.

But you're going further than that.  What's the theory here?
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