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

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radix tree.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@27356 a95241bf-73f2-0310-859d-f6bbb57e9c96
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Ingo Weinhold 2008-09-07 13:58:49 +00:00
parent dcadb2ba8d
commit c909ca65bf
1 changed files with 6 additions and 8 deletions
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docs/develop/kernel/swap_file_support
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@ -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 Because in this way, we can easily tell if two adjacent pages are in a same
swap file. (See the code in VMAnonymousCache::Read()). swap file. (See the code in VMAnonymousCache::Read()).
Each swap file has a linear bitmap, and all pages in the swap file are The efficiency of the FreeBSD swap system lies in a special data structure:
associated with a bit in the bitmap. When the page is used, the corresponding radix bitmap(i.e. bitmap using radix tree for hinting.) It can operate well no
bit is set to 1 and when free, it is set to 0. The linear bitmap is different matter how much fragmentation there is and no matter how large a bitmap is
from FreeBSD. FreeBSD uses a radix bitmap and it's more efficient than linear used. I have ported the radix bitmap structure to Haiku, so our swap system
bitmap especially when swap space is fragmented. The reason why I did not use will have a good performance. More information on radix bitmap, please look
a radix bitmap is I do not get a total understanding of radix tree structure at the source code.
currently. But I will replace the linear bitmap with radix bitmap in the
future.
Swap space allocation takes place when we swap anonymous pages out. Swap space allocation takes place when we swap anonymous pages out.
In order to make the allocation less probable to fail, anonymous cache will In order to make the allocation less probable to fail, anonymous cache will