On Thu, Aug 30, 2012 at 06:36:12PM +0800, Shaohua Li wrote:
> On Mon, Aug 27, 2012 at 06:52:07PM +0400, Konstantin Khlebnikov wrote:
> > >--- 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.
>
> makes sense. vma->anon_vma could be NUll (shmem), but in shmem
> case, vma could NULL too, so maybe just ignore it.
>
>
> Subject: swap: add a simple random read swapin detection
>
> 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%
>
> 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
>
> V2->V3:
> move swapra_miss to 'struct anon_vma' as suggested by Konstantin.
>
> 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/rmap.h | 3 +++
> mm/internal.h | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++
> mm/memory.c | 3 ++-
> mm/shmem.c | 1 +
> mm/swap_state.c | 6 ++++++
> 5 files changed, 62 insertions(+), 1 deletion(-)
>
> Index: linux/mm/swap_state.c
> ===================================================================
> --- linux.orig/mm/swap_state.c 2012-08-29 16:13:00.912112140 +0800
> +++ linux/mm/swap_state.c 2012-08-30 18:28:24.678315187 +0800
> @@ -20,6 +20,7 @@
> #include <linux/page_cgroup.h>
>
> #include <asm/pgtable.h>
> +#include "internal.h"
>
> /*
> * swapper_space is a fiction, retained to simplify the path through
> @@ -379,6 +380,10 @@ struct page *swapin_readahead(swp_entry_
> unsigned long mask = (1UL << page_cluster) - 1;
> struct blk_plug plug;
>
> + swap_cache_miss(vma);
> + if (swap_cache_skip_readahead(vma))
> + goto skip;
> +
> /* Read a page_cluster sized and aligned cluster around offset. */
> start_offset = offset & ~mask;
> end_offset = offset | mask;
> @@ -397,5 +402,6 @@ struct page *swapin_readahead(swp_entry_
> blk_finish_plug(&plug);
>
> lru_add_drain(); /* Push any new pages onto the LRU now */
> +skip:
> return read_swap_cache_async(entry, gfp_mask, vma, addr);
> }
> Index: linux/mm/memory.c
> ===================================================================
> --- linux.orig/mm/memory.c 2012-08-29 16:13:00.920112040 +0800
> +++ linux/mm/memory.c 2012-08-30 13:32:05.425830660 +0800
> @@ -2953,7 +2953,8 @@ static int do_swap_page(struct mm_struct
> ret = VM_FAULT_HWPOISON;
> delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
> goto out_release;
> - }
> + } else if (!(flags & FAULT_FLAG_TRIED))
> + swap_cache_hit(vma);
>
> locked = lock_page_or_retry(page, mm, flags);
>
> Index: linux/mm/internal.h
> ===================================================================
> --- linux.orig/mm/internal.h 2012-08-29 16:13:00.932111888 +0800
> +++ linux/mm/internal.h 2012-08-30 18:28:03.698578951 +0800
> @@ -12,6 +12,7 @@
> #define __MM_INTERNAL_H
>
> #include <linux/mm.h>
> +#include <linux/rmap.h>
>
> void free_pgtables(struct mmu_gather *tlb, struct vm_area_struct *start_vma,
> unsigned long floor, unsigned long ceiling);
> @@ -356,3 +357,52 @@ extern unsigned long vm_mmap_pgoff(struc
> unsigned long, unsigned long);
>
> extern void set_pageblock_order(void);
> +
> +/*
> + * Unnecessary readahead harms performance. 1. for SSD, big size read is more
> + * expensive than small size read, so extra unnecessary read only has overhead.
> + * For harddisk, this overhead doesn't exist. 2. unnecessary readahead will
> + * allocate extra memroy, which further tights memory pressure, so more
> + * swapout/swapin.
> + * These adds a simple swap random access detection. In swap page fault, if
> + * page is found in swap cache, decrease an account of vma, otherwise we need
> + * do sync swapin and the account is increased. Optionally swapin will do
> + * readahead if the counter is below a threshold.
> + */
> +#ifdef CONFIG_SWAP
> +#define SWAPRA_MISS (100)
> +static inline void swap_cache_hit(struct vm_area_struct *vma)
> +{
> + if (vma && vma->anon_vma)
> + atomic_dec_if_positive(&vma->anon_vma->swapra_miss);
> +}
> +
> +static inline void swap_cache_miss(struct vm_area_struct *vma)
> +{
> + if (!vma || !vma->anon_vma)
> + return;
> + if (atomic_read(&vma->anon_vma->swapra_miss) < SWAPRA_MISS * 10)
You can use some meaningful macro instead of magic vaule 10.
/*
* If swapra_miss is higher than SWAPRA_SKIP_THRESHOLD, swapin readahead
* will be skipped.
* swapra_miss count could be increased until SWAPRA_MISS_MAX_COUNT.
* If swapra_miss count is decreased by SWAPRA_SKIP_THRESHOLD below
* by cache hit, we can start swapin readahead, again.
*/
#define SWAPRA_SKIP_THRESHOLD 100
#define SWAPRA_MISS_MAX_COUNT (SWAPRA_SKIP_THRESHOLD * 10)
> + atomic_inc(&vma->anon_vma->swapra_miss);
> +}
> +
> +static inline int swap_cache_skip_readahead(struct vm_area_struct *vma)
> +{
> + if (!vma || !vma->anon_vma)
> + return 0;
> + return atomic_read(&vma->anon_vma->swapra_miss) > SWAPRA_MISS;
> +}
> +#else
> +static inline void swap_cache_hit(struct vm_area_struct *vma)
> +{
> +}
> +
> +static inline void swap_cache_miss(struct vm_area_struct *vma)
> +{
> +}
> +
> +static inline int swap_cache_skip_readahead(struct vm_area_struct *vma)
> +{
> + return 0;
> +}
> +
> +#endif
> Index: linux/include/linux/rmap.h
> ===================================================================
> --- linux.orig/include/linux/rmap.h 2012-06-01 10:10:31.686394463 +0800
> +++ linux/include/linux/rmap.h 2012-08-30 18:10:12.256048781 +0800
> @@ -35,6 +35,9 @@ struct anon_vma {
> * anon_vma if they are the last user on release
> */
> atomic_t refcount;
> +#ifdef CONFIG_SWAP
> + atomic_t swapra_miss;
> +#endif
>
> /*
> * NOTE: the LSB of the head.next is set by
> Index: linux/mm/shmem.c
> ===================================================================
> --- linux.orig/mm/shmem.c 2012-08-06 16:00:45.465441525 +0800
> +++ linux/mm/shmem.c 2012-08-30 18:10:51.755553250 +0800
> @@ -933,6 +933,7 @@ static struct page *shmem_swapin(swp_ent
> pvma.vm_pgoff = index + info->vfs_inode.i_ino;
> pvma.vm_ops = NULL;
> pvma.vm_policy = spol;
> + pvma.anon_vma = NULL;
So, shmem always do readahead blindly still?
> return swapin_readahead(swap, gfp, &pvma, 0);
> }
>
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