linux-kernel - Re: [PATCH] mm: skip reserved page for kmem leak scanning

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Date:   Tue, 30 Aug 2022 10:41:43 +0800
From:   Zhaoyang Huang <huangzhaoyang@...il.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     "zhaoyang.huang" <zhaoyang.huang@...soc.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        "open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>, Ke Wang <ke.wang@...soc.com>
Subject: Re: [PATCH] mm: skip reserved page for kmem leak scanning

On Mon, Aug 29, 2022 at 8:19 PM David Hildenbrand <david@...hat.com> wrote:
>
> On 26.08.22 05:23, Zhaoyang Huang wrote:
> > On Fri, Aug 26, 2022 at 11:13 AM zhaoyang.huang
> > <zhaoyang.huang@...soc.com> wrote:
> >>
> >> From: Zhaoyang Huang <zhaoyang.huang@...soc.com>
> >>
> >> It is no need to scan reserved page, skip it.
> >>
> >> Signed-off-by: Zhaoyang Huang <zhaoyang.huang@...soc.com>
> >> ---
> >>  mm/kmemleak.c | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/mm/kmemleak.c b/mm/kmemleak.c
> >> index a182f5d..c546250 100644
> >> --- a/mm/kmemleak.c
> >> +++ b/mm/kmemleak.c
> >> @@ -1471,7 +1471,7 @@ static void kmemleak_scan(void)
> >>                         if (page_zone(page) != zone)
> >>                                 continue;
> >>                         /* only scan if page is in use */
> >> -                       if (page_count(page) == 0)
> >> +                       if (page_count(page) == 0 || PageReserved(page))
> > Sorry for previous stupid code by my faint, correct it here
>
> Did you even test the initial patch?
>
> I wonder why we should consider this change
>
> (a) I doubt it's a performance issue. If it is, please provide numbers
>     before/after.
For Android-like SOC systems where AP(cpu runs linux) are one of the
memory consumers which are composed of other processors such as modem,
isp,wcn etc. The reserved memory occupies a certain number of
memory(could be 30% of MemTotal) which makes scan reserved pages
pointless.
> (b) We'll stop scanning early allocations. As the memmap is usually
>     allocated early during boot ... we'll stop scanning essentially the
>     whole mmap and that whole loop would be dead code? What am i
>     missing?
memmap refers to pages here? If we can surpass these as it exist
permanently during life period. Besides, I wonder if PageLRU should
also be skipped?
-                       if (page_count(page) == 0)
+                       if (page_count(page) == 0 ||
PageReserved(page) || PageLRU(page))
>
> --
> Thanks,
>
> David / dhildenb
>