Messages in this thread |  | | Date | Fri, 25 May 2001 16:53:38 -0300 (BRST) | From | Rik van Riel <> | Subject | [PATCH] highmem deadlock removal, balancing & cleanup |
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Hi Linus,
the following patch does:
1) Remove GFP_BUFFER and HIGHMEM related deadlocks, by letting these allocations fail instead of looping forever in __alloc_pages() when they cannot make any progress there.
Now Linux no longer hangs on highmem machines with heavy write loads.
2) Clean up the __alloc_pages() / __alloc_pages_limit() code a bit, moving the direct reclaim condition from the latter function into the former so we run it less often ;)
3) Remove the superfluous wakeups from __alloc_pages(), not only are the tests a real CPU eater, they also have the potential of waking up bdflush in a situation where it shouldn't run in the first place. The kswapd wakeup didn't seem to have any effect either.
4) Do make sure GFP_BUFFER allocations NEVER eat into the very last pages of the system. It is important to preserve the following ordering: - normal allocations - GFP_BUFFER - atomic allocations - other recursive allocations
Using this ordering, we can be pretty sure that eg. a GFP_BUFFER allocation to swap something out to an encrypted device won't eat the memory the device driver will need to perform its functions. It also means that a gigabit network flood won't eat those pages...
5) Change nr_free_buffer_pages() a bit to not return pages which cannot be used as buffer pages, this makes a BIG difference on highmem machines (which now DO have a working write throttling again).
6) Simplify the refill_inactive() loop enough that it actually works again. Calling page_launder() and shrink_i/d_memory() by the same if condition means that the different caches get balanced against each other again.
The illogical argument for not shrinking the slab cache while we're under a free shortage turned out to be very much illogical too. All needed buffer heads will have been allocated in page_launder() and shrink_i/d_memory() before we get here and we can be pretty sure that these functions will keep re-using those same buffer heads as soon as the IO finishes.
regards,
Rik -- Linux MM bugzilla: http://linux-mm.org/bugzilla.shtml
Virtual memory is like a game you can't win; However, without VM there's truly nothing to lose...
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