Messages in this thread | | | Date | Sat, 13 Jan 2007 15:51:42 +1100 | From | Nick Piggin <> | Subject | Re: O_DIRECT question |
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Bill Davidsen wrote:
> The point is that if you want to be able to allocate at all, sometimes > you will have to write dirty pages, garbage collect, and move or swap > programs. The hardware is just too limited to do something less painful, > and the user can't see memory to do things better. Linus is right, > 'Claiming that there is a "proper solution" is usually a total red > herring. Quite often there isn't, and the "paper over" is actually not > papering over, it's quite possibly the best solution there is.' I think > any solution is going to be ugly, unfortunately.
It seems quite robust and clean to me, actually. Any userspace memory that absolutely must be large contiguous regions have to be allocated at boot or from a pool reserved at boot. All other allocations can be broken into smaller ones.
Write dirty pages, garbage collect, move or swap programs isn't going to be robust because there is lots of vital kernel memory that cannot be moved and will cause fragmentation.
The reclaimable zone work that went on a while ago for hugepages is exactly how you would also fix this problem and still have a reasonable degree of flexibility at runtime. It isn't really ugly or hard, compared with some of the non-working "solutions" that have been proposed.
The other good thing is that the core mm already has practically everything required, so the functionality is unintrusive.
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