[OpenAFS] Re: Windows cache rehashed...
Jeffrey Altman
jaltman@columbia.edu
Wed, 17 Dec 2003 12:54:27 -0500
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You can read information about the CreateFileMapping() API within the
MSDN library.
The memory associated with the file mapping is allocated as
PAGE_READWRITE with the
default section attribute (SEC_COMMIT):
SEC_COMMIT Allocates physical storage in memory or in the paging file
on disk for all pages of a section. This is the default setting.
SEC_IMAGE The file specified for a section's file mapping is an
executable image file. Because the mapping information and file
protection are taken from the image file, no other attributes are valid
with SEC_IMAGE.
*Windows Me/98/95: *This flag is not supported.
SEC_NOCACHE All pages of a section are to be set as noncacheable. This
attribute is intended for architectures requiring various locking
structures to be in memory that is never fetched into the processor's.
On 80x86 and MIPS machines, using the cache for these structures only
slows down the performance as the hardware keeps the caches coherent.
Some device drivers require noncached data so that programs can write
through to the physical memory. SEC_NOCACHE requires either the
SEC_RESERVE or SEC_COMMIT to also be set.
SEC_RESERVE Reserves all pages of a section without allocating physical
storage. The reserved range of pages cannot be used by any other
allocation operations until it is released. Reserved pages can be
committed in subsequent calls to the *VirtualAlloc* function. This
attribute is valid only if the /hFile/ parameter is
INVALID_HANDLE_VALUE; that is, a file mapping object backed by the
operating system paging file.
Joe Buehler wrote:
> OK, thanks -- the cache file is mmap'd by afsd and it depends on Windows
> to manage what's in RAM.
>
> The question arose because of a peculiarity of Task Manager under
> Windows NT.
> It shows "memory usage" for afsd being about the size of the cache, but
> "virtual memory" stays small. So I guess Task Manager has a couple
> things
> mixed up, or they have defined some terms strangely.
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You can read information about the CreateFileMapping() API within the
MSDN library.<br>
The memory associated with the file mapping is allocated as
PAGE_READWRITE with the<br>
default section attribute (SEC_COMMIT):<br>
<br>
<br>
<table>
<tbody>
<tr>
<td width="40%">SEC_COMMIT</td>
<td width="60%">Allocates physical storage in memory or in the
paging file on disk for all pages of a section. This is the default
setting.</td>
</tr>
<tr>
<td width="40%">SEC_IMAGE</td>
<td width="60%">The file specified for a section's file mapping
is an executable image file. Because the mapping information and file
protection are taken from the image file, no other attributes are valid
with SEC_IMAGE.
<p></p>
<p><b>Windows Me/98/95: </b>This flag is not supported.</p>
</td>
</tr>
<tr>
<td width="40%">SEC_NOCACHE</td>
<td width="60%">All pages of a section are to be set as
noncacheable. This attribute is intended for architectures requiring
various locking structures to be in memory that is never fetched into
the processor's. On 80x86 and MIPS machines, using the cache for these
structures only slows down the performance as the hardware keeps the
caches coherent. Some device drivers require noncached data so that
programs can write through to the physical memory. SEC_NOCACHE requires
either the SEC_RESERVE or SEC_COMMIT to also be set.</td>
</tr>
<tr>
<td width="40%">SEC_RESERVE</td>
<td width="60%">Reserves all pages of a section without
allocating physical storage. The reserved range of pages cannot be used
by any other allocation operations until it is released. Reserved pages
can be committed in subsequent calls to the <MSHelp:link tabindex="0"
keywords="base.virtualalloc" errorurl="../common/badjump.htm"><b>VirtualAlloc</b></MSHelp:link>
function. This attribute is valid only if the <i>hFile</i> parameter
is INVALID_HANDLE_VALUE; that is, a file mapping object backed by the
operating system paging file.</td>
</tr>
</tbody>
</table>
<br>
<br>
Joe Buehler wrote:<br>
<blockquote cite="mid3FDF721A.6020101@hekimian.com" type="cite">OK,
thanks -- the cache file is mmap'd by afsd and it depends on Windows
<br>
to manage what's in RAM.
<br>
<br>
The question arose because of a peculiarity of Task Manager under
Windows NT.
<br>
It shows "memory usage" for afsd being about the size of the cache, but
<br>
"virtual memory" stays small. So I guess Task Manager has a couple
things
<br>
mixed up, or they have defined some terms strangely.
<br>
</blockquote>
</body>
</html>
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