Re: [PATCH 1/1] mm: smaps: split PSS into components

[Andrew Morton <akpm@linux-foundation.org>]

On Wed, 26 Jun 2019 11:04:29 -0700 semenzato@chromium.org wrote:

> From: Luigi Semenzato <semenzato@chromium.org>
> 
> Report separate components (anon, file, and shmem)
> for PSS in smaps_rollup.
> 
> This helps understand and tune the memory manager behavior
> in consumer devices, particularly mobile devices.  Many of
> them (e.g. chromebooks and Android-based devices) use zram
> for anon memory, and perform disk reads for discarded file
> pages.  The difference in latency is large (e.g. reading
> a single page from SSD is 30 times slower than decompressing
> a zram page on one popular device), thus it is useful to know
> how much of the PSS is anon vs. file.
> 
> This patch also removes a small code duplication in smaps_account,
> which would have gotten worse otherwise.
> 
> Also added missing entry for smaps_rollup in
> Documentation/filesystems/proc.txt.
> 
> ...
>
> -static void __show_smap(struct seq_file *m, const struct mem_size_stats *mss)
> +static void __show_smap(struct seq_file *m, const struct mem_size_stats *mss,
> +	bool rollup_mode)
>  {
>  	SEQ_PUT_DEC("Rss:            ", mss->resident);
>  	SEQ_PUT_DEC(" kB\nPss:            ", mss->pss >> PSS_SHIFT);
> +	if (rollup_mode) {
> +		/*
> +		 * These are meaningful only for smaps_rollup, otherwise two of
> +		 * them are zero, and the other one is the same as Pss.
> +		 */
> +		SEQ_PUT_DEC(" kB\nPss_Anon:       ",
> +			mss->pss_anon >> PSS_SHIFT);
> +		SEQ_PUT_DEC(" kB\nPss_File:       ",
> +			mss->pss_file >> PSS_SHIFT);
> +		SEQ_PUT_DEC(" kB\nPss_Shmem:      ",
> +			mss->pss_shmem >> PSS_SHIFT);
> +	}

Documentation/filesystems/proc.txt is rather incomplete.  It documents
/proc/PID/smaps (seems to be out of date) but doesn't describe the
fields in smaps_rollup.

Please update Documentation/ABI/testing/procfs-smaps_rollup and please
check that it's up-to-date while you're in there.