Hi, Kazu
Thank you for the comment.
On Wed, Feb 15, 2023 at 1:38 PM HAGIO KAZUHITO(萩尾 一仁) <k-hagio...@nec.com>
wrote:
> On 2023/02/14 23:37, Lianbo Jiang wrote:
> > The "kmem -i" option may output the bogus statistics of CACHED, which
> > might be observed when some extreme situations occur in kernel, such as
> > OOM, disk IO errors, etc.
> >
> > The following result of calculation may be a negative value, refer to
> > the dump_kmeminfo():
> > page_cache_size = nr_file_pages - swapper_space_nrpages -
> buffer_pages;
> >
> > As a result, the negative value will be converted to unsigned long
> > integer, eventually it overflows and gets a big integer.
> >
> > crash> kmem -i
> > PAGES TOTAL PERCENTAGE
> > TOTAL MEM 255314511 973.9 GB ----
> > FREE 533574 2 GB 0% of TOTAL MEM
> > USED 254780937 971.9 GB 99% of TOTAL MEM
> > SHARED 1713 6.7 MB 0% of TOTAL MEM
> > BUFFERS 374 1.5 MB 0% of TOTAL MEM
> > CACHED -114 70368744177664 GB 72251060080% of TOTAL MEM
> > ^^^^ ^^^^^^^^^^^^^^ ^^^^^^^^^^^^
>
> I think that this is not very bad output :) because we can notice
> the negative value. Maybe it's due to future kernel changes.
>
>
It's true. But it is also easy to mislead users, because it is not clear
whether the crash tool
gave a wrong result.
Actually this issue was observed on the kernel 3.10.
So if you set it to zero, what about emitting an info message?
>
>
It should be good to have an info message.
> + if (page_cache_size < 0) {
> + error(INFO, "page_cache_size went negative (%ld), setting
> to 0\n",
> + page_cache_size);
> + page_cache_size = 0;
> + }
>
>
Looks good.
Thanks.
Lianbo
> For example,
>
> crash> kmem -i
> PAGES TOTAL PERCENTAGE
> TOTAL MEM 16252500 62 GB ----
> FREE 246162 961.6 MB 1% of TOTAL MEM
> USED 16006338 61.1 GB 98% of TOTAL MEM
> SHARED 329258 1.3 GB 2% of TOTAL MEM
> BUFFERS 1436 5.6 MB 0% of TOTAL MEM
> kmem: page_cache_size went negative (-114), setting to 0
> CACHED 0 0 0% of TOTAL MEM
> SLAB 311514 1.2 GB 1% of TOTAL MEM
>
> Thanks,
> Kazu
>
> > ...
> >
> > Let's normalize it to zero to fix such corner cases.
> >
> > Reported-by: Buland Kumar Singh <bsi...@redhat.com>
> > Signed-off-by: Lianbo Jiang <liji...@redhat.com>
> > ---
> > memory.c | 2 ++
> > 1 file changed, 2 insertions(+)
> >
> > diff --git a/memory.c b/memory.c
> > index e0742c1bd3a4..860a3a978a4d 100644
> > --- a/memory.c
> > +++ b/memory.c
> > @@ -8615,6 +8615,8 @@ dump_kmeminfo(void)
> > page_cache_size = 0;
> >
> >
> > + if (page_cache_size < 0)
> > + page_cache_size = 0;
> > pct = (page_cache_size * 100)/totalram_pages;
> > fprintf(fp, "%13s %7ld %11s %3ld%% of TOTAL MEM\n",
> > "CACHED", page_cache_size,
--
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