From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f180.google.com (mail-pd0-f180.google.com [209.85.192.180]) by kanga.kvack.org (Postfix) with ESMTP id 15CC96B0038 for ; Thu, 12 Jun 2014 17:48:02 -0400 (EDT) Received: by mail-pd0-f180.google.com with SMTP id ft15so1387581pdb.39 for ; Thu, 12 Jun 2014 14:48:01 -0700 (PDT) Received: from mailuogwdur.emc.com (mailuogwdur.emc.com. [128.221.224.79]) by mx.google.com with ESMTPS id kc2si42852596pbc.148.2014.06.12.14.48.00 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Thu, 12 Jun 2014 14:48:00 -0700 (PDT) Received: from maildlpprd55.lss.emc.com (maildlpprd55.lss.emc.com [10.106.48.159]) by mailuogwprd54.lss.emc.com (Sentrion-MTA-4.3.0/Sentrion-MTA-4.3.0) with ESMTP id s5CLlxOa002517 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO) for ; Thu, 12 Jun 2014 17:47:59 -0400 Received: from mailusrhubprd52.lss.emc.com (mailusrhubprd52.lss.emc.com [10.106.48.25]) by maildlpprd55.lss.emc.com (RSA Interceptor) for ; Thu, 12 Jun 2014 17:47:44 -0400 Received: from mxhub40.corp.emc.com (mxhub40.corp.emc.com [128.222.70.107]) by mailusrhubprd52.lss.emc.com (Sentrion-MTA-4.3.0/Sentrion-MTA-4.3.0) with ESMTP id s5CLlieu008788 (version=TLSv1/SSLv3 cipher=AES128-SHA bits=128 verify=FAIL) for ; Thu, 12 Jun 2014 17:47:44 -0400 From: "Alkalay, Amitai" Date: Thu, 12 Jun 2014 17:47:42 -0400 Subject: kernel mem_map reservation with hugepages Message-ID: Content-Language: en-US Content-Type: multipart/alternative; boundary="_000_E01DC0E960CD0F49B63BFEE7FBA569971125F1D1C0MX16Acorpemcc_" MIME-Version: 1.0 Sender: owner-linux-mm@kvack.org List-ID: To: "linux-mm@kvack.org" --_000_E01DC0E960CD0F49B63BFEE7FBA569971125F1D1C0MX16Acorpemcc_ Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Hi, According to this page about 1.36% = of the system memory is reserved to mem_map (I confirmed it before in the c= ode - I saw that the kernel indeed saves a struct of 65 bytes for each page= , meaning 63 structs per page). I have a server (CentOS6) with 256GB of RAM, so it means that the kernel r= eserves about 4GB for mem_map. Most of the pages in my server are hugepages, using the kernel command line= argument "hugepages=3DX". I believe this means that the kernel can reserve a much smaller amount of m= emory for the mappings - since there are much less pages (i.e. if all pages= are huges it can reserve 8MB instead of 4GB). Am I right? Any suggestions if and how it can be done? Thanks, Amitai --_000_E01DC0E960CD0F49B63BFEE7FBA569971125F1D1C0MX16Acorpemcc_ Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

 

Hi,

 = ;

According to this page about 1.36% of the system memory is rese= rved to mem_map (I confirmed it before in the= code – I saw that the kernel indeed saves a struct of 65 byte= s for each page, meaning 63 structs per page)= .

I have a server (CentOS6) with = 256GB of RAM,  so it means that the kernel reserves about 4GB for mem_= map.

Most of the pages in my server are h= ugepages, using the kernel command line argument “hugepages=3DX”= ;.

I belie= ve this means that the kernel can reserve a much smaller amount of m= emory for the mappings – since there are much less pages (i.e. if all= pages are huges it can reserve 8MB instead of 4GB).

 

Am I right?

Any sugges= tions if and how it can be done?

&n= bsp;

Thanks,

Amitai

 

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