Shaohua Li wrote:
The swapin readahead does a blind readahead regardless if the swapin is
sequential. This is ok for harddisk and random read, because read big size has
no penality in harddisk, and if the readahead pages are garbage, they can be
reclaimed fastly. But for SSD, big size read is more expensive than small size
read. If readahead pages are garbage, such readahead only has overhead.
This patch addes a simple random read detection like what file mmap readahead
does. If random read is detected, swapin readahead will be skipped. This
improves a lot for a swap workload with random IO in a fast SSD.
I run anonymous mmap write micro benchmark, which will triger swapin/swapout.
runtime changes with path
randwrite harddisk -38.7%
seqwrite harddisk -1.1%
randwrite SSD -46.9%
seqwrite SSD +0.3%
Very nice!
For both harddisk and SSD, the randwrite swap workload run time is reduced
significant. sequential write swap workload hasn't chanage.
Interesting is the randwrite harddisk test is improved too. This might be
because swapin readahead need allocate extra memory, which further tights
memory pressure, so more swapout/swapin.
This patch depends on readahead-fault-retry-breaks-mmap-file-read-random-detection.patch
V1->V2:
1. Move the swap readahead accounting to separate functions as suggested by Riel.
2. Enable the logic only with CONFIG_SWAP enabled as suggested by Minchan.
Signed-off-by: Shaohua Li<shli@xxxxxxxxxxxx>
---
include/linux/mm_types.h | 3 +++
mm/internal.h | 44 ++++++++++++++++++++++++++++++++++++++++++++
mm/memory.c | 3 ++-
mm/swap_state.c | 8 ++++++++
4 files changed, 57 insertions(+), 1 deletion(-)
--- linux.orig/include/linux/mm_types.h 2012-08-22 11:44:53.077912855 +0800
+++ linux/include/linux/mm_types.h 2012-08-24 13:07:11.798576941 +0800
@@ -279,6 +279,9 @@ struct vm_area_struct {
#ifdef CONFIG_NUMA
struct mempolicy *vm_policy; /* NUMA policy for the VMA */
#endif
+#ifdef CONFIG_SWAP
+ atomic_t swapra_miss;
+#endif
You can place this atomic on vma->anon_vma, it has perfect 4-byte hole right
after field "refcount". vma->anon_vma already exists since this vma already
contains anon pages.
};
struct core_thread {
--
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