Re: [Crash-utility] [PATCH] display MCNT and PRIVATE when using kmem -p
Hello Dave,
I think it is necessary to see what is hided in the union where
_mapcount lies. However, as you said, it's hard to pick which fields are
more important than others when adding new items to "kmem -p". So I
think over using struct sub-command to show what I want.
What if I change struct sub-command to this:
1. it can refer to anonymous members (e.g., page._mapcount)
2. it can refer to submembers(e.g., page._count.counter)
3. it can output easy-parsing format (using an option to specify), maybe
like 'kmem -p'. For example,
crash> struct page.flags,_count.counter -.. < PAGE_list.txt
1024 0
1024 1
1024 1
1024 1
After adding these features to struct sub-command, I guess it is more
easier to get information hiding in structs and parsing it. Before
implementing, I feel the necessity to ask you for some advices. So what
about these features?
At 2012-1-6 3:37, Dave Anderson wrote:
I appreciate the effort, but I'm not sure whether it's worth
changing
it at this point, or whether it could be accomplished in a different
manner.
The primary purpose for "kmem -p" is to show the page structure
address associated with each physical address in the system -- along
with "basic information about each page". It's had those basic
fields in it forever -- which BTW, fit into 80 columns. I prefer not
to have command output exceed 80 columns unless it is impossible to
predict the size of an output field.
Anyway, the page structure definition keeps changing over time, more
specifically the embedded anonymous structures contained within it, and
the fields within the anonymous structs have multiple meanings. With
your patch, the output becomes cluttered and hard to understand, especially
due to the strange values that can be seen in the MCNT column when it's
not a counter value, but rather a slab-page construct:
union {
atomic_t _mapcount;
struct {
unsigned inuse:16;
unsigned objects:15;
unsigned frozen:1;
};
};
And so it's hard to pick which fields are more important than others,
because it pretty much depends upon what's being debugged. You have
picked the private field (which can have numerous meanings), but for
example, there have been times in the past where I wanted to see the
lru list_head contents.
That all being said, your patch does have merit, but I wonder if there
could be an alternate way of selecting or filtering what fields are
displayed?
--
--
Regards
Qiao Nuohan