Why not copy around data in physical RAM?
Posted Sep 9, 2005 1:14 UTC (Fri) by mmarq
In reply to: Why not copy around data in physical RAM?
Parent article: Kswapd and high-order allocations
i'm not a kernel hacker either... just a curious that try to understand, so...
"Most pointers contain the virtual address of some memory area, those don't matter. But some actually contain the physical or bus address... If you tried to move those pages around, you'd have a lot of fun handling the random application coredumps and occasional kernel panic. "
Just dont move them!... but there are many bits residing in physical memory that are obvious candidates, that shouldn't get in the way of those that cannot be moved or vice-versa. Is it something really stupid to advocate the creation of memory pools adressable by the kernel ?
My idea(stupid or not) is that pages marked as "obvious candidates" for swap should not be imediately swaped but trowned "defragmented" to a *reserved* portion of physical memory, very usefull because i suspect each time more truth that what is swapable now could be absolutely required next second in a highly CPU context swaping of 'highly threaded' world of applications and services... thus making kswapd lasy and stop him from wasting useful CPU cicles better used by a proper defragmentation code.
Other idea is that disk cache, should always be created as two separeted physical memory pools, program and data. Better, a *program cache pool* should be created, requiring that program bits 'should' enter this pool already in a *continuous order*, that is defragmented(and this is possible because programs bits only change when are upgraded,i.e. almost never in CPU time!), and not trowned in the general physical memory space 'highly competition' pool for any 4K page of physical memory, when or where ever available.
This program cache is certainly not a hot requirement for server systems, but could be a killer feature for workstation/desktop, because differently from a RAMDisk it would be quicker and more versatile as in the possibility of making their size hot dynamic, holding defragmented program bits from not only any required runtime but also other executables from /bin, /usr/bin or /usr/sbin scheduled from a simple algorithm, based on simple parameters as many times runned and usefulness.
Belive none of this will deprecate server performance, and in the middle you should get a much bigger pool of continously adressable memory pages.
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