Messages in this thread | | | Date | Wed, 19 May 1999 18:28:04 +0200 (CEST) | From | Andrea Arcangeli <> | Subject | Re: [VFS] move active filesystem |
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On Tue, 18 May 1999, Chris Wedgwood wrote:
>> And what about a more inteligent DMA memory allocator ? I mean, in >> case of fragmented memory it's very frequent not to success to >> allocate DMA memory by kernel (eg by sound/floppy modules). Why >> does not kernel moves some memory, changing some pagetable entries >> etc to create contigous memory area suitable for DMA (in low 16M >> for ISA DMA, care of page boundaries etc). If there's enough memory >> to do it, it would be only some memory moving action to get the >> suitable place. >> >> (I don't know too much about Linux kernel internals, maybe DMA >> memory allocating is something atomic operation which blocks the >> kernel too long to do such an operation I described below ?) > >Right now, we can't tell which pages are in use by what, so moving
Not really. We obviously can, but not in O(1). I could just add the logic to have the information in O(1), but then you must know that at every allocation you'll have to insert a entry in a queue, and remove an entry from a queue at every umapping/freeing of memory. Anyway I'll think I'll do that very soon to improve and simplify a lot my update_shared_mappings and many other similar thing in order to handle all such things in O(1). (and btw with such info my new shrink_mmap will be also able to unmap and free page/swap cache directly from the pagemap-lru (I am talking about my current code, the stock kernel doesn't have a real lru))
BTW, allowing dirty pages in the page cache may avoid I/O to disk but won't avoid memcpy data to the page cache even if the page cache was just uptdate. So I am convinced right now update_shared_mappings() is the right thing to do and it's not an dirty hack. It's only a not very efficient implementation that has to play with pgd/pmd/pte because we don't have enough information (yet) from the pagemap.
Andrea Arcangeli
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