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From: Andi Kleen <ak@linux.intel.com>
To: Chunsheng Luo <luochunsheng@ustc.edu>
Cc: gregkh@linuxfoundation.org,  rafael@kernel.org,
  akpm@linux-foundation.org,  linux-kernel@vger.kernel.org,
  linux-mm@kvack.org
Subject: Re: [PATCH] meminfo: provide estimated per-node's available memory
In-Reply-To: <20240204083414.107799-1-luochunsheng@ustc.edu> (Chunsheng Luo's
	message of "Sun, 4 Feb 2024 03:34:14 -0500")
References: <20240204083414.107799-1-luochunsheng@ustc.edu>
Date: Fri, 09 Feb 2024 01:56:03 -0800
Message-ID: <87fry2t0zw.fsf@linux.intel.com>
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Chunsheng Luo <luochunsheng@ustc.edu> writes:

> +	available = sum_zone_node_page_state(nid, NR_FREE_PAGES) - pgdat->totalreserve_pages;
> +
> +	/*
> +	 * Not all the page cache can be freed, otherwise the system will
> +	 * start swapping or thrashing. Assume at least half of the page
> +	 * cache, or the low watermark worth of cache, needs to stay.
> +	 */
> +	pagecache = node_page_state(pgdat, NR_ACTIVE_FILE) +
> +		node_page_state(pgdat, NR_INACTIVE_FILE);
> +	pagecache -= min(pagecache / 2, wmark_low);


The magic number 2 should be a define (or maybe even a tunable). Similar
below. It seems quite arbitrary, but I don't have a better solution
either. Maybe could handle dirty differently, but nothing stands out here


> +		node_page_state(pgdat, NR_KERNEL_MISC_RECLAIMABLE);
> +	reclaimable -= min(reclaimable / 2, wmark_low);
> +	available += reclaimable;
> +
> +	if (available < 0)
> +		available = 0;

That would be a bug? Perhaps add a WARN_ON


With those changes:

Reviewed-by: Andi Kleen <ak@linux.intel.com>


-Andi