mm, swap: skip swapcache for swapin of synchronous device

With fast swap storage, the platforms want to use swap more aggressively
and swap-in is crucial to application latency.

The rw_page() based synchronous devices like zram, pmem and btt are such
fast storage.  When I profile swapin performance with zram lz4
decompress test, S/W overhead is more than 70%.  Maybe, it would be
bigger in nvdimm.

This patch aims to reduce swap-in latency by skipping swapcache if the
swap device is synchronous device like rw_page based device.  It
enhances 45% my swapin test(5G sequential swapin, no readahead, from
2.41sec to 1.64sec).

Link: http://lkml.kernel.org/r/1505886205-9671-5-git-send-email-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Ilya Dryomov <idryomov@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Huang Ying <ying.huang@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 933d7c0..32c06f0 100644 (file)
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -466,6 +466,7 @@ extern int page_swapcount(struct page *);
 extern int __swp_swapcount(swp_entry_t entry);
 extern int swp_swapcount(swp_entry_t entry);
 extern struct swap_info_struct *page_swap_info(struct page *);
+extern struct swap_info_struct *swp_swap_info(swp_entry_t entry);
 extern bool reuse_swap_page(struct page *, int *);
 extern int try_to_free_swap(struct page *);
 struct backing_dev_info;
@@ -474,6 +475,16 @@ extern void exit_swap_address_space(unsigned int type);
 
 #else /* CONFIG_SWAP */
 
+static inline int swap_readpage(struct page *page, bool do_poll)
+{
+       return 0;
+}
+
+static inline struct swap_info_struct *swp_swap_info(swp_entry_t entry)
+{
+       return NULL;
+}
+
 #define swap_address_space(entry)              (NULL)
 #define get_nr_swap_pages()                    0L
 #define total_swap_pages                       0L

diff --git a/mm/memory.c b/mm/memory.c
index cae514e..f75bff2 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2842,7 +2842,7 @@ EXPORT_SYMBOL(unmap_mapping_range);
 int do_swap_page(struct vm_fault *vmf)
 {
        struct vm_area_struct *vma = vmf->vma;
-       struct page *page = NULL, *swapcache;
+       struct page *page = NULL, *swapcache = NULL;
        struct mem_cgroup *memcg;
        struct vma_swap_readahead swap_ra;
        swp_entry_t entry;
@@ -2881,17 +2881,35 @@ int do_swap_page(struct vm_fault *vmf)
                }
                goto out;
        }
+
+
        delayacct_set_flag(DELAYACCT_PF_SWAPIN);
        if (!page)
                page = lookup_swap_cache(entry, vma_readahead ? vma : NULL,
                                         vmf->address);
        if (!page) {
-               if (vma_readahead)
-                       page = do_swap_page_readahead(entry,
-                               GFP_HIGHUSER_MOVABLE, vmf, &swap_ra);
-               else
-                       page = swapin_readahead(entry,
-                               GFP_HIGHUSER_MOVABLE, vma, vmf->address);
+               struct swap_info_struct *si = swp_swap_info(entry);
+
+               if (!(si->flags & SWP_SYNCHRONOUS_IO)) {
+                       if (vma_readahead)
+                               page = do_swap_page_readahead(entry,
+                                       GFP_HIGHUSER_MOVABLE, vmf, &swap_ra);
+                       else
+                               page = swapin_readahead(entry,
+                                       GFP_HIGHUSER_MOVABLE, vma, vmf->address);
+                       swapcache = page;
+               } else {
+                       /* skip swapcache */
+                       page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, vmf->address);
+                       if (page) {
+                               __SetPageLocked(page);
+                               __SetPageSwapBacked(page);
+                               set_page_private(page, entry.val);
+                               lru_cache_add_anon(page);
+                               swap_readpage(page, true);
+                       }
+               }
+
                if (!page) {
                        /*
                         * Back out if somebody else faulted in this pte
@@ -2920,7 +2938,6 @@ int do_swap_page(struct vm_fault *vmf)
                goto out_release;
        }
 
-       swapcache = page;
        locked = lock_page_or_retry(page, vma->vm_mm, vmf->flags);
 
        delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
@@ -2935,7 +2952,8 @@ int do_swap_page(struct vm_fault *vmf)
         * test below, are not enough to exclude that.  Even if it is still
         * swapcache, we need to check that the page's swap has not changed.
         */
-       if (unlikely(!PageSwapCache(page) || page_private(page) != entry.val))
+       if (unlikely((!PageSwapCache(page) ||
+                       page_private(page) != entry.val)) && swapcache)
                goto out_page;
 
        page = ksm_might_need_to_copy(page, vma, vmf->address);
@@ -2988,14 +3006,16 @@ int do_swap_page(struct vm_fault *vmf)
                pte = pte_mksoft_dirty(pte);
        set_pte_at(vma->vm_mm, vmf->address, vmf->pte, pte);
        vmf->orig_pte = pte;
-       if (page == swapcache) {
-               do_page_add_anon_rmap(page, vma, vmf->address, exclusive);
-               mem_cgroup_commit_charge(page, memcg, true, false);
-               activate_page(page);
-       } else { /* ksm created a completely new copy */
+
+       /* ksm created a completely new copy */
+       if (unlikely(page != swapcache && swapcache)) {
                page_add_new_anon_rmap(page, vma, vmf->address, false);
                mem_cgroup_commit_charge(page, memcg, false, false);
                lru_cache_add_active_or_unevictable(page, vma);
+       } else {
+               do_page_add_anon_rmap(page, vma, vmf->address, exclusive);
+               mem_cgroup_commit_charge(page, memcg, true, false);
+               activate_page(page);
        }
 
        swap_free(entry);
@@ -3003,7 +3023,7 @@ int do_swap_page(struct vm_fault *vmf)
            (vma->vm_flags & VM_LOCKED) || PageMlocked(page))
                try_to_free_swap(page);
        unlock_page(page);
-       if (page != swapcache) {
+       if (page != swapcache && swapcache) {
                /*
                 * Hold the lock to avoid the swap entry to be reused
                 * until we take the PT lock for the pte_same() check
@@ -3036,7 +3056,7 @@ out_page:
        unlock_page(page);
 out_release:
        put_page(page);
-       if (page != swapcache) {
+       if (page != swapcache && swapcache) {
                unlock_page(swapcache);
                put_page(swapcache);
        }

diff --git a/mm/page_io.c b/mm/page_io.c
index cd52b9c..e93f1a4 100644 (file)
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -347,7 +347,7 @@ out:
        return ret;
 }
 
-int swap_readpage(struct page *page, bool do_poll)
+int swap_readpage(struct page *page, bool synchronous)
 {
        struct bio *bio;
        int ret = 0;
@@ -355,7 +355,7 @@ int swap_readpage(struct page *page, bool do_poll)
        blk_qc_t qc;
        struct gendisk *disk;
 
-       VM_BUG_ON_PAGE(!PageSwapCache(page), page);
+       VM_BUG_ON_PAGE(!PageSwapCache(page) && !synchronous, page);
        VM_BUG_ON_PAGE(!PageLocked(page), page);
        VM_BUG_ON_PAGE(PageUptodate(page), page);
        if (frontswap_load(page) == 0) {
@@ -403,7 +403,7 @@ int swap_readpage(struct page *page, bool do_poll)
        count_vm_event(PSWPIN);
        bio_get(bio);
        qc = submit_bio(bio);
-       while (do_poll) {
+       while (synchronous) {
                set_current_state(TASK_UNINTERRUPTIBLE);
                if (!READ_ONCE(bio->bi_private))
                        break;

diff --git a/mm/swapfile.c b/mm/swapfile.c
index cb08fa6..85aff8a 100644 (file)
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -3455,10 +3455,15 @@ int swapcache_prepare(swp_entry_t entry)
        return __swap_duplicate(entry, SWAP_HAS_CACHE);
 }
 
+struct swap_info_struct *swp_swap_info(swp_entry_t entry)
+{
+       return swap_info[swp_type(entry)];
+}
+
 struct swap_info_struct *page_swap_info(struct page *page)
 {
-       swp_entry_t swap = { .val = page_private(page) };
-       return swap_info[swp_type(swap)];
+       swp_entry_t entry = { .val = page_private(page) };
+       return swp_swap_info(entry);
 }
 
 /*
@@ -3466,7 +3471,6 @@ struct swap_info_struct *page_swap_info(struct page *page)
  */
 struct address_space *__page_file_mapping(struct page *page)
 {
-       VM_BUG_ON_PAGE(!PageSwapCache(page), page);
        return page_swap_info(page)->swap_file->f_mapping;
 }
 EXPORT_SYMBOL_GPL(__page_file_mapping);
@@ -3474,7 +3478,6 @@ EXPORT_SYMBOL_GPL(__page_file_mapping);
 pgoff_t __page_file_index(struct page *page)
 {
        swp_entry_t swap = { .val = page_private(page) };
-       VM_BUG_ON_PAGE(!PageSwapCache(page), page);
        return swp_offset(swap);
 }
 EXPORT_SYMBOL_GPL(__page_file_index);