linux-kernel - Re: Linux 5.9-rc7 / VmallocTotal wrongly reported

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Message-ID: <20201001203931.GD2706729@carbon.DHCP.thefacebook.com>
Date:   Thu, 1 Oct 2020 13:39:31 -0700
From:   Roman Gushchin <guro@...com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
CC:     Bastian Bittorf <bb@....de>, Vlastimil Babka <vbabka@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Shakeel Butt <shakeelb@...gle.com>
Subject: Re: Linux 5.9-rc7 / VmallocTotal wrongly reported

On Thu, Oct 01, 2020 at 12:58:36PM -0700, Linus Torvalds wrote:
> On Thu, Oct 1, 2020 at 12:56 PM Roman Gushchin <guro@...com> wrote:
> >
> > Bastian, can you, please, share your config?
> 
> Bastian actually did that in the original email, but that was only
> sent to me and Andrew in private.
> 
> Here's that config replicated for your pleasure,

Thank you!

> 
> #
> # Processor type and features
> #
> # CONFIG_ZONE_DMA is not set
> # CONFIG_SMP is not set

Yes, here is the deal.

The SMP-version of __mod_node_page_state() converts a passed value from bytes
to pages, but the non-SMP doesn't.

Thanks!


--

>From 3d0233b37340c78012b991d3570b92f91cf5ebd2 Mon Sep 17 00:00:00 2001
From: Roman Gushchin <guro@...com>
Date: Thu, 1 Oct 2020 13:07:49 -0700
Subject: [PATCH] mm: memcg/slab: fix slab statistics in !SMP configuration

Since ea426c2a7de8 ("mm: memcg: prepare for byte-sized vmstat items")
the write side of slab counters accepts a value in bytes and converts
it to pages. It happens in __mod_node_page_state().

However a non-SMP version of __mod_node_page_state() doesn't perform
this conversion. It leads to incorrect (unrealistically high) slab
counters values. Fix this by adding a similar conversion to the
non-SMP version of __mod_node_page_state().

Signed-off-by: Roman Gushchin <guro@...com>
Reported-by: Bastian Bittorf <bb@....de>
Fixes: ea426c2a7de8 ("mm: memcg: prepare for byte-sized vmstat items")
---
 include/linux/vmstat.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
index d5431c1bf6e5..322dcbfcc933 100644
--- a/include/linux/vmstat.h
+++ b/include/linux/vmstat.h
@@ -312,6 +312,11 @@ static inline void __mod_zone_page_state(struct zone *zone,
 static inline void __mod_node_page_state(struct pglist_data *pgdat,
 			enum node_stat_item item, int delta)
 {
+	if (vmstat_item_in_bytes(item)) {
+		VM_WARN_ON_ONCE(delta & (PAGE_SIZE - 1));
+		delta >>= PAGE_SHIFT;
+	}
+
 	node_page_state_add(delta, pgdat, item);
 }
 
-- 
2.26.2