Messages in this thread | | | Date | Mon, 29 Nov 1999 15:05:40 +0100 (CET) | From | Andrea Arcangeli <> | Subject | Re: Large memory question |
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On Mon, 29 Nov 1999, Matthew Kirkwood wrote:
>How does the swap cache fit into this picture? Is that obsolete
The swap cache is just a cache for the swap area. It doesn't make any difference for the VM to have the swap cache or not. The swap cache has as the offset/index field of the page set with the contents of the not present pte. Then at fault time we just do a search on the cache for such a pte before starting I/O so we can avoid major faults. It allows us to do async swapout cleanly. The other good thing of the swap cache is that if there is a swapin read fault then we map the page cache in userspace (exactly as we do with the page cache for private mappings) and then if such page must be swapped out again we only need to unmap the page cache and write to the pte the value of the page->offset/index and we don't need to I/O to swapout such page again (because the swap cache took the swap entry busy and we know that the swap still contains the data of the page).
It's only a cache from/to the swap as the pagecache is for the disk.
>(or absent) under 2.3 now?
It's still present of course.
Andrea
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