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Date:   Wed, 15 Jun 2022 13:57:56 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Vincent Whitchurch <vincent.whitchurch@axis.com>
Cc:     <kernel@axis.com>, <linux-mm@kvack.org>,
        <linux-kernel@vger.kernel.org>, <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH] mm/smaps: add Pss_Dirty
Message-Id: <20220615135756.ddc3341239b739d5f1f88da6@linux-foundation.org>
In-Reply-To: <20220615071252.1153408-1-vincent.whitchurch@axis.com>
References: <20220615071252.1153408-1-vincent.whitchurch@axis.com>
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On Wed, 15 Jun 2022 09:12:52 +0200 Vincent Whitchurch <vincent.whitchurch@axis.com> wrote:

> Pss is the sum of the sizes of clean and dirty private pages, and the
> proportional sizes of clean and dirty shared pages:
> 
>  Private = Private_Dirty + Private_Clean
>  Shared_Proportional = Shared_Dirty_Proportional + Shared_Clean_Proportional
>  Pss = Private + Shared_Proportional
> 
> The Shared*Proportional fields are not present in smaps, so it is not
> possible to determine how much of the Pss is from dirty pages and how
> much is from clean pages.  This information can be useful for measuring
> memory usage for the purpose of optimisation, since clean pages can
> usually be discarded by the kernel immediately while dirty pages cannot.
> 
> The smaps routines in the kernel already have access to this data, so
> add a Pss_Dirty to show it to userspace.  Pss_Clean is not added since
> it can be calculated from Pss and Pss_Dirty.
> 
> ...
>
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -406,6 +406,7 @@ struct mem_size_stats {
>  	u64 pss_anon;
>  	u64 pss_file;
>  	u64 pss_shmem;
> +	u64 pss_dirty;
>  	u64 pss_locked;
>  	u64 swap_pss;
>  };
> @@ -427,6 +428,7 @@ static void smaps_page_accumulate(struct mem_size_stats *mss,
>  		mss->pss_locked += pss;
>  
>  	if (dirty || PageDirty(page)) {
> +		mss->pss_dirty += pss;
>  		if (private)
>  			mss->private_dirty += size;
>  		else
> @@ -820,6 +822,7 @@ static void __show_smap(struct seq_file *m, const struct mem_size_stats *mss,
>  		SEQ_PUT_DEC(" kB\nPss_Shmem:      ",
>  			mss->pss_shmem >> PSS_SHIFT);
>  	}
> +	SEQ_PUT_DEC(" kB\nPss_Dirty:      ", mss->pss_dirty >> PSS_SHIFT);
>  	SEQ_PUT_DEC(" kB\nShared_Clean:   ", mss->shared_clean);
>  	SEQ_PUT_DEC(" kB\nShared_Dirty:   ", mss->shared_dirty);
>  	SEQ_PUT_DEC(" kB\nPrivate_Clean:  ", mss->private_clean);

Well it's certainly simple.

Can you please update Documentation/ABI/testing/procfs-smaps_rollup and
Documentation/filesystems/proc.rst, resend?