linux-kernel - Re: Sudden and massive page cache eviction

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Message-ID: <AANLkTi=PXoMA0gv53_7h16u1259sh1uOxg2cSXYSXThv@mail.gmail.com>
Date:	Wed, 24 Nov 2010 19:46:28 +0200
From:	Pekka Enberg <penberg@...nel.org>
To:	Peter Schüller <scode@...tify.com>
Cc:	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Mattias de Zalenski <zalenski@...tify.com>,
	linux-mm@...ck.org
Subject: Re: Sudden and massive page cache eviction

Hi Peter,

2010/11/24 Peter Schüller <scode@...tify.com>:
>>> I forgot to address the second part of this question: How would I best
>>> inspect whether the kernel is doing that?
>>
>> You can, for example, record
>>
>>  cat /proc/meminfo | grep Huge
>>
>> for large page allocations.
>
> Those show zero a per my other post. However I got the impression Dave
> was asking about regular but larger-than-one-page allocations internal
> to the kernel, while the Huge* lines in /proc/meminfo refers to
> allocations specifically done by userland applications doing huge page
> allocation on a system with huge pages enabled - or am I confused?

He was asking about both (large page allocations and higher order allocations).

>> The "pagesperslab" column of /proc/slabinfo tells you how many pages
>> slab allocates from the page allocator.
>
> Seems to be what vmstat -m reports.

No, "vmstat -m" reports _total number_ of pages allocated. We're
interested in how many pages slab allocator whenever it needs to
allocate memory for a new slab. That's represented by the
"pagesperslab" column of /proc/slabinfo from which you can deduce the
page allocation order.

                        Pekka
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