Re: [PATCH 1/1] pagemap clear_refs: modify to specify anon or mapped vma clearing

[Moussa Ba]

Mel,

here are two scripts that make use of the interface to "measure"
Referenced anon vs. mapped pages.

save the awk script to refs.awk  and run the bash script as follows

./refscount PID secs

PID is the process you want to monitor while secs is the number of
seconds to sleep before clearing the refs.    The output after x secs
is a the total number of refs before and immediately after clearing.
Here is an example run using firefox as I was writing this email.

/usr/lib/firefox-3.0.3/firefox
12:10:58 Mapped = 12856 kB Anon = 27896 kB
12:10:58 Mapped = 760 kB Anon = 4 kB
12:11:08 Mapped = 5884 kB Anon = 20340 kB
.
.
.
.
12:16:19 Mapped = 476 kB Anon = 0 kB
12:16:29 Mapped = 7016 kB Anon = 13128 kB
12:16:29 Mapped = 476 kB Anon = 0 kB
12:16:39 Mapped = 9276 kB Anon = 21588 kB
12:16:39 Mapped = 476 kB Anon = 0 kB
12:16:49 Mapped = 10288 kB Anon = 16000 kB
12:16:49 Mapped = 716 kB Anon = 12 kB

BEGIN BASH SCRIPT
--------------------------------
#!/bin/bash

echo `cat /proc/$1/cmdline`
#Intial state of the process
cat /proc/$1/smaps | awk -f refs.awk

while [ true ]
do
    echo 1 > /proc/$1/clear_refs
    # Immidiately after clearing
    cat /proc/$1/smaps | awk -f refs.awk
    sleep $2
    # after x seconds
    cat /proc/$1/smaps | awk -f refs.awk
done
---------------------------
END BASH SCRIPT

BEGIN AWK SCRIPT
-----------------------

BEGIN {refsanon = 0;refsmapped=0;}

{
    if (NF == 6)  {
	if ($4 == "00:00")
	    type = 1;
	else
	    type = 2;
    }

    if ($1 == "Referenced:") {
	if (type == 1)
	    refsanon += $2;
	if (type == 2)
	    refsmapped += $2;
	type = 0;
    }

}
END {printf("%s ",strftime("%H:%M:%S"));  print "Mapped = " refsmapped
" kB Anon = " refsanon " kB";}

---------------------------
END AWK SCRIPT


On Wed, Jul 29, 2009 at 7:58 AM, Mel Gorman<mel@xxxxxxxxx> wrote:
> On Tue, Jul 28, 2009 at 05:00:54PM -0700, Moussa Ba wrote:
>> The patch makes the clear_refs more versatile in adding the option to
>> select anonymous pages or file backed pages for clearing.  This
>> addition has a measurable impact on user space application performance
>> as it decreases the number of pagewalks in scenarios where one is only
>> interested in a specific type of page (anonymous or file mapped).
>>
>
> I think what Andrew might be looking for is a repeat of the use-case for
> using clear_refs at all and what the additional usecase is that makes this
> patch beneficial. To be honest, I had to go digging for a bit to find out
> why clear_refs is used at all and the potential benefits of this patch were
> initially unclear to me although they were obvious to others. I confess I
> haven't read the patch closely to determine if it's behaving as advertised
> or not.
>
> Bonus points for a wee illustration of a script that measures the apparent
> working set of a process using clear_refs, showing the working set for anon
> vs filebacked and the difference of measuring just anon versus the full
> process for example. Such a script could be added to Documentation/vm as
> I didn't spot any example in there already.
>
> Total aside, is there potential to really mess with LRU aging by abusing
> clear_refs a lot, partcularly as clear_refs is writable by the process
> owner? Does it matter?
>
>>
>> On Tue, Jul 28, 2009 at 4:52 PM, Andrew Morton<akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
>> > On Tue, 28 Jul 2009 15:52:05 -0700
>> > "Moussa A. Ba" <moussa.a.ba@xxxxxxxxx> wrote:
>> >
>> >> This patch adds anonymous and file backed filters to the clear_refs interface.
>> >> echo 1 > /proc/PID/clear_refs resets the bits on all pages
>> >> echo 2 > /proc/PID/clear_refs resets the bits on anonymous pages only
>> >> echo 3 > /proc/PID/clear_refs resets the bits on file backed pages only
>> >> Any other value is ignored
>> >
>> > The changelog is missing any rationale for making this change.
>> > Originally we were told that it "makes the clear_refs proc interface a
>> > bit more versatile", but that's a bit thin.
>> >
>> > How do we justify making this change to Linux?  What value does it
>> > have?  Can you describe a usage scenario which would help people
>> > understand the usefulness of the change?
>> >
>> > Thanks.
>> >
>>
>
> --
> Mel Gorman
> Part-time Phd Student                          Linux Technology Center
> University of Limerick                         IBM Dublin Software Lab
>
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