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d03853d566
It turns out that our current __hash_page code will do a very hot busy-wait loop waiting on _PAGE_BUSY to be cleared. It even does ldarx/stdcx in the loop, which will bounce reservations around like crazy if there's more than one CPU spinning on the same PTE (or even another PTE in the same reservation granule). The end result is that each fault takes longer when there's contention, which in turn increases the chance of another thread hitting the same fault and also piling up. Not pretty. There's two options here: 1. Do an out-of-line busy loop a'la spinlocks with just loads (no reserves) 2. Just bail and refault if needed. (2) makes sense here: If the PTE is busy, chances are it's in flux anyway and the other code path making a change might just be ready to hash it. This fixes a stampede seen on a large-ish system where a multithreaded HPC app faults in the same text pages on several cpus at the same time. Signed-off-by: Olof Johansson <olof@lixom.net> Cc: Paul Mackerras <paulus@samba.org> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org> |
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