Aren/haiku
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Patch by Zhao Shuai: Updated documentation regarding the use of the

Browse Source 
radix tree.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@27356 a95241bf-73f2-0310-859d-f6bbb57e9c96
This commit is contained in:
Ingo Weinhold 2008-09-07 13:58:49 +00:00
parent dcadb2ba8d
commit c909ca65bf
1 changed files with 6 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
docs/develop/kernel/swap_file_support
View File

@ -72,14 +72,12 @@ swap file is: 0-99, 101-200, 202-301) Why leave a page gap between swap files?
Because in this way, we can easily tell if two adjacent pages are in a same
swap file. (See the code in VMAnonymousCache::Read()).
Each swap file has a linear bitmap, and all pages in the swap file are
associated with a bit in the bitmap. When the page is used, the corresponding
bit is set to 1 and when free, it is set to 0. The linear bitmap is different
from FreeBSD. FreeBSD uses a radix bitmap and it's more efficient than linear
bitmap especially when swap space is fragmented. The reason why I did not use
a radix bitmap is I do not get a total understanding of radix tree structure
currently. But I will replace the linear bitmap with radix bitmap in the
future.
The efficiency of the FreeBSD swap system lies in a special data structure:
radix bitmap(i.e. bitmap using radix tree for hinting.) It can operate well no
matter how much fragmentation there is and no matter how large a bitmap is
used. I have ported the radix bitmap structure to Haiku, so our swap system
will have a good performance. More information on radix bitmap, please look
at the source code.
Swap space allocation takes place when we swap anonymous pages out.
In order to make the allocation less probable to fail, anonymous cache will