• Andy Whitcroft's avatar
    sparsemem: clean up spelling error in comments · cd881a6b
    Andy Whitcroft authored
    SPARSEMEM is a pretty nice framework that unifies quite a bit of code over all
    the arches.  It would be great if it could be the default so that we can get
    rid of various forms of DISCONTIG and other variations on memory maps.  So far
    what has hindered this are the additional lookups that SPARSEMEM introduces
    for virt_to_page and page_address.  This goes so far that the code to do this
    has to be kept in a separate function and cannot be used inline.
    
    This patch introduces a virtual memmap mode for SPARSEMEM, in which the memmap
    is mapped into a virtually contigious area, only the active sections are
    physically backed.  This allows virt_to_page page_address and cohorts become
    simple shift/add operations.  No page flag fields, no table lookups, nothing
    involving memory is required.
    
    The two key operations pfn_to_page and page_to_page become:
    
       #define __pfn_to_page(pfn)      (vmemmap + (pfn))
       #define __page_to_pfn(page)     ((page) - vmemmap)
    
    By having a virtual mapping for the memmap we allow simple access without
    wasting physical memory.  As kernel memory is typically already mapped 1:1
    this introduces no additional overhead.  The virtual mapping must be big
    enough to allow a struct page to be allocated and mapped for all valid
    physical pages.  This vill make a virtual memmap difficult to use on 32 bit
    platforms that support 36 address bits.
    
    However, if there is enough virtual space available and the arch already maps
    its 1-1 kernel space using TLBs (f.e.  true of IA64 and x86_64) then this
    technique makes SPARSEMEM lookups even more efficient than CONFIG_FLATMEM.
    FLATMEM needs to read the contents of the mem_map variable to get the start of
    the memmap and then add the offset to the required entry.  vmemmap is a
    constant to which we can simply add the offset.
    
    This patch has the potential to allow us to make SPARSMEM the default (and
    even the only) option for most systems.  It should be optimal on UP, SMP and
    NUMA on most platforms.  Then we may even be able to remove the other memory
    models: FLATMEM, DISCONTIG etc.
    
    The current aim is to bring a common virtually mapped mem_map to all
    architectures.  This should facilitate the removal of the bespoke
    implementations from the architectures.  This also brings performance
    improvements for most architecture making sparsmem vmemmap the more desirable
    memory model.  The ultimate aim of this work is to expand sparsemem support to
    encompass all the features of the other memory models.  This could allow us to
    drop support for and remove the other models in the longer term.
    
    Below are some comparitive kernbench numbers for various architectures,
    comparing default memory model against SPARSEMEM VMEMMAP.  All but ia64 show
    marginal improvement; we expect the ia64 figures to be sorted out when the
    larger mapping support returns.
    
    x86-64 non-NUMA
                 Base    VMEMAP    % change (-ve good)
    User        85.07     84.84    -0.26
    System      34.32     33.84    -1.39
    Total      119.38    118.68    -0.59
    
    ia64
                 Base    VMEMAP    % change (-ve good)
    User      1016.41   1016.93    0.05
    System      50.83     51.02    0.36
    Total     1067.25   1067.95    0.07
    
    x86-64 NUMA
                 Base   VMEMAP    % change (-ve good)
    User        30.77   431.73     0.22
    System      45.39    43.98    -3.11
    Total      476.17   475.71    -0.10
    
    ppc64
                 Base   VMEMAP    % change (-ve good)
    User       488.77   488.35    -0.09
    System      56.92    56.37    -0.97
    Total      545.69   544.72    -0.18
    
    Below are some AIM bencharks on IA64 and x86-64 (thank Bob).  The seems
    pretty much flat as you would expect.
    
    ia64 results 2 cpu non-numa 4Gb SCSI disk
    
    Benchmark	Version	Machine	Run Date
    AIM Multiuser Benchmark - Suite VII	"1.1"	extreme	Jun  1 07:17:24 2007
    
    Tasks	Jobs/Min	JTI	Real	CPU	Jobs/sec/task
    1	98.9		100	58.9	1.3	1.6482
    101	5547.1		95	106.0	79.4	0.9154
    201	6377.7		95	183.4	158.3	0.5288
    301	6932.2		95	252.7	237.3	0.3838
    401	7075.8		93	329.8	316.7	0.2941
    501	7235.6		94	403.0	396.2	0.2407
    600	7387.5		94	472.7	475.0	0.2052
    
    Benchmark	Version	Machine	Run Date
    AIM Multiuser Benchmark - Suite VII	"1.1"	vmemmap	Jun  1 09:59:04 2007
    
    Tasks	Jobs/Min	JTI	Real	CPU	Jobs/sec/task
    1	99.1		100	58.8	1.2	1.6509
    101	5480.9		95	107.2	79.2	0.9044
    201	6490.3		95	180.2	157.8	0.5382
    301	6886.6		94	254.4	236.8	0.3813
    401	7078.2		94	329.7	316.0	0.2942
    501	7250.3		95	402.2	395.4	0.2412
    600	7399.1		94	471.9	473.9	0.2055
    
    open power 710 2 cpu, 4 Gb, SCSI and configured physically
    
    Benchmark	Version	Machine	Run Date
    AIM Multiuser Benchmark - Suite VII	"1.1"	extreme	May 29 15:42:53 2007
    
    Tasks	Jobs/Min	JTI	Real	CPU	Jobs/sec/task
    1	25.7		100	226.3	4.3	0.4286
    101	1096.0		97	536.4	199.8	0.1809
    201	1236.4		96	946.1	389.1	0.1025
    301	1280.5		96	1368.0	582.3	0.0709
    401	1270.2		95	1837.4	771.0	0.0528
    501	1251.4		96	2330.1	955.9	0.0416
    601	1252.6		96	2792.4	1139.2	0.0347
    701	1245.2		96	3276.5	1334.6	0.0296
    918	1229.5		96	4345.4	1728.7	0.0223
    
    Benchmark	Version	Machine	Run Date
    AIM Multiuser Benchmark - Suite VII	"1.1"	vmemmap	May 30 07:28:26 2007
    
    Tasks	Jobs/Min	JTI	Real	CPU	Jobs/sec/task
    1	25.6		100	226.9	4.3	0.4275
    101	1049.3		97	560.2	198.1	0.1731
    201	1199.1		97	975.6	390.7	0.0994
    301	1261.7		96	1388.5	591.5	0.0699
    401	1256.1		96	1858.1	771.9	0.0522
    501	1220.1		96	2389.7	955.3	0.0406
    601	1224.6		96	2856.3	1133.4	0.0340
    701	1252.0		96	3258.7	1314.1	0.0298
    915	1232.8		96	4319.7	1704.0	0.0225
    
    amd64 2 2-core, 4Gb and SATA
    
    Benchmark	Version	Machine	Run Date
    AIM Multiuser Benchmark - Suite VII	"1.1"	extreme	Jun  2 03:59:48 2007
    
    Tasks	Jobs/Min	JTI	Real	CPU	Jobs/sec/task
    1	13.0		100	446.4	2.1	0.2173
    101	533.4		97	1102.0	110.2	0.0880
    201	578.3		97	2022.8	220.8	0.0480
    301	583.8		97	3000.6	332.3	0.0323
    401	580.5		97	4020.1	442.2	0.0241
    501	574.8		98	5072.8	558.8	0.0191
    600	566.5		98	6163.8	671.0	0.0157
    
    Benchmark	Version	Machine	Run Date
    AIM Multiuser Benchmark - Suite VII	"1.1"	vmemmap	Jun  3 04:19:31 2007
    
    Tasks	Jobs/Min	JTI	Real	CPU	Jobs/sec/task
    1	13.0		100	447.8	2.0	0.2166
    101	536.5		97	1095.6	109.7	0.0885
    201	567.7		97	2060.5	219.3	0.0471
    301	582.1		96	3009.4	330.2	0.0322
    401	578.2		96	4036.4	442.4	0.0240
    501	585.1		98	4983.2	555.1	0.0195
    600	565.5		98	6175.2	660.6	0.0157
    
    This patch:
    
    Fix some spelling errors.
    Signed-off-by: default avatarChristoph Lameter <clameter@sgi.com>
    Signed-off-by: default avatarAndy Whitcroft <apw@shadowen.org>
    Acked-by: default avatarMel Gorman <mel@csn.ul.ie>
    Cc: "Luck, Tony" <tony.luck@intel.com>
    Cc: Andi Kleen <ak@suse.de>
    Cc: "David S. Miller" <davem@davemloft.net>
    Cc: Paul Mackerras <paulus@samba.org>
    Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
    Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    cd881a6b
sparse.c 8.28 KB