linux-kernel - Re: [PATCH RFC] mm, proc: add PcpFree to meminfo

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Date:   Tue, 16 Aug 2022 20:03:35 +0800
From:   Kefeng Wang <wangkefeng.wang@...wei.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:     Andrew Morton <akpm@...ux-foundation.org>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>, Liu Shixin <liushixin2@...wei.com>,
        "Vlastimil Babka" <vbabka@...e.cz>,
        David Hildenbrand <david@...hat.com>,
        Shakeel Butt <shakeelb@...gle.com>
Subject: Re: [PATCH RFC] mm, proc: add PcpFree to meminfo


On 2022/8/16 18:50, Greg Kroah-Hartman wrote:
> On Tue, Aug 16, 2022 at 06:11:18PM +0800, Kefeng Wang wrote:
>> On 2022/8/16 17:16, Greg Kroah-Hartman wrote:
>>> On Tue, Aug 16, 2022 at 04:44:26PM +0800, Kefeng Wang wrote:
>>>> From: Liu Shixin <liushixin2@...wei.com>
>>>>
>>>> The page on pcplist could be used, but not counted into memory free or
>>>> avaliable, and pcp_free is only showed by show_mem(). Since commit
>>>> d8a759b57035 ("mm, page_alloc: double zone's batchsize"), there is a
>>>> significant decrease in the display of free memory, with a large number
>>>> of cpus and nodes, the number of pages in the percpu list can be very
>>>> large, so it is better to let user to know the pcp count.
>>>>
>>>> Signed-off-by: Liu Shixin <liushixin2@...wei.com>
>>>> Signed-off-by: Kefeng Wang <wangkefeng.wang@...wei.com>
>>>> ---
>>>>    drivers/base/node.c | 14 +++++++++++++-
>>>>    fs/proc/meminfo.c   |  9 +++++++++
>>>>    2 files changed, 22 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/base/node.c b/drivers/base/node.c
>>>> index eb0f43784c2b..846864e45db6 100644
>>>> --- a/drivers/base/node.c
>>>> +++ b/drivers/base/node.c
>>>> @@ -375,6 +375,9 @@ static ssize_t node_read_meminfo(struct device *dev,
>>>>    	struct sysinfo i;
>>>>    	unsigned long sreclaimable, sunreclaimable;
>>>>    	unsigned long swapcached = 0;
>>>> +	unsigned long free_pcp = 0;
>>>> +	struct zone *zone;
>>>> +	int cpu;
>>>>    	si_meminfo_node(&i, nid);
>>>>    	sreclaimable = node_page_state_pages(pgdat, NR_SLAB_RECLAIMABLE_B);
>>>> @@ -382,9 +385,17 @@ static ssize_t node_read_meminfo(struct device *dev,
>>>>    #ifdef CONFIG_SWAP
>>>>    	swapcached = node_page_state_pages(pgdat, NR_SWAPCACHE);
>>>>    #endif
>>>> +	for_each_populated_zone(zone) {
>>>> +		if (zone_to_nid(zone) != nid)
>>>> +			continue;
>>>> +		for_each_online_cpu(cpu)
>>>> +			free_pcp += per_cpu_ptr(zone->per_cpu_pageset, cpu)->count;
>>>> +	}
>>>> +
>>>>    	len = sysfs_emit_at(buf, len,
>>>>    			    "Node %d MemTotal:       %8lu kB\n"
>>>>    			    "Node %d MemFree:        %8lu kB\n"
>>>> +			    "Node %d PcpFree:        %8lu kB\n"
>>> First off, this sysfs file is a huge violation of the normal sysfs
>>> rules, so I will not allow any new entries to be added.  In fact, the
>>> whole thing should just be removed and multiple files created in its
>>> place.
>> Hi Greg, do you mean to remove all /sys/devices/system/node/node*/meminfo,
>>
>> but this will beak ABI, is it acceptable?
> I do not know, what tool relies on this file?  Any userspace tool should
> always be able to handle a sysfs file being removed, so you should
> probably work with the tool authors to fix this up before removing it.

https://github.com/numactl/numactl/blob/93867c59b0bb29470873a427dc7f06ebaf305221/numastat.c#L841

It seems numastat use this file, but there are maybe more tools,

Cc'ed more mm experts to see more comments.

>
> thanks,
>
> gre gk-h
> .