From: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx> Subject: mm/swap: allocate swap slots in batches Currently, the swap slots are allocated one page at a time, causing contention to the swap_info lock protecting the swap partition on every page being swapped. This patch adds new functions get_swap_pages and scan_swap_map_slots to request multiple swap slots at once. This will reduces the lock contention on the swap_info lock. Also scan_swap_map_slots can operate more efficiently as swap slots often occurs in clusters close to each other on a swap device and it is quicker to allocate them together. Link: http://lkml.kernel.org/r/9fec2845544371f62c3763d43510045e33d286a6.1484082593.git.tim.c.chen@xxxxxxxxxxxxxxx Signed-off-by: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx> Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx> Cc: Aaron Lu <aaron.lu@xxxxxxxxx> Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> Cc: Christian Borntraeger <borntraeger@xxxxxxxxxx> Cc: Dave Hansen <dave.hansen@xxxxxxxxx> Cc: Hillf Danton <hillf.zj@xxxxxxxxxxxxxxx> Cc: Huang Ying <ying.huang@xxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Jonathan Corbet <corbet@xxxxxxx> escreveu: Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxxxx> Cc: Minchan Kim <minchan@xxxxxxxxxx> Cc: Rik van Riel <riel@xxxxxxxxxx> Cc: Shaohua Li <shli@xxxxxxxxxx> Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/linux/swap.h | 2 mm/swapfile.c | 136 +++++++++++++++++++++++++++++++++-------- 2 files changed, 113 insertions(+), 25 deletions(-) diff -puN include/linux/swap.h~mm-swap-allocate-swap-slots-in-batches include/linux/swap.h --- a/include/linux/swap.h~mm-swap-allocate-swap-slots-in-batches +++ a/include/linux/swap.h @@ -27,6 +27,7 @@ struct bio; #define SWAP_FLAGS_VALID (SWAP_FLAG_PRIO_MASK | SWAP_FLAG_PREFER | \ SWAP_FLAG_DISCARD | SWAP_FLAG_DISCARD_ONCE | \ SWAP_FLAG_DISCARD_PAGES) +#define SWAP_BATCH 64 static inline int current_is_kswapd(void) { @@ -386,6 +387,7 @@ static inline long get_nr_swap_pages(voi extern void si_swapinfo(struct sysinfo *); extern swp_entry_t get_swap_page(void); extern swp_entry_t get_swap_page_of_type(int); +extern int get_swap_pages(int n, swp_entry_t swp_entries[]); extern int add_swap_count_continuation(swp_entry_t, gfp_t); extern void swap_shmem_alloc(swp_entry_t); extern int swap_duplicate(swp_entry_t); diff -puN mm/swapfile.c~mm-swap-allocate-swap-slots-in-batches mm/swapfile.c --- a/mm/swapfile.c~mm-swap-allocate-swap-slots-in-batches +++ a/mm/swapfile.c @@ -496,7 +496,7 @@ scan_swap_map_ssd_cluster_conflict(struc * Try to get a swap entry from current cpu's swap entry pool (a cluster). This * might involve allocating a new cluster for current CPU too. */ -static void scan_swap_map_try_ssd_cluster(struct swap_info_struct *si, +static bool scan_swap_map_try_ssd_cluster(struct swap_info_struct *si, unsigned long *offset, unsigned long *scan_base) { struct percpu_cluster *cluster; @@ -520,7 +520,7 @@ new_cluster: *scan_base = *offset = si->cluster_next; goto new_cluster; } else - return; + return false; } found_free = false; @@ -552,16 +552,22 @@ new_cluster: cluster->next = tmp + 1; *offset = tmp; *scan_base = tmp; + return found_free; } -static unsigned long scan_swap_map(struct swap_info_struct *si, - unsigned char usage) +static int scan_swap_map_slots(struct swap_info_struct *si, + unsigned char usage, int nr, + swp_entry_t slots[]) { struct swap_cluster_info *ci; unsigned long offset; unsigned long scan_base; unsigned long last_in_cluster = 0; int latency_ration = LATENCY_LIMIT; + int n_ret = 0; + + if (nr > SWAP_BATCH) + nr = SWAP_BATCH; /* * We try to cluster swap pages by allocating them sequentially @@ -579,8 +585,10 @@ static unsigned long scan_swap_map(struc /* SSD algorithm */ if (si->cluster_info) { - scan_swap_map_try_ssd_cluster(si, &offset, &scan_base); - goto checks; + if (scan_swap_map_try_ssd_cluster(si, &offset, &scan_base)) + goto checks; + else + goto scan; } if (unlikely(!si->cluster_nr--)) { @@ -624,8 +632,14 @@ static unsigned long scan_swap_map(struc checks: if (si->cluster_info) { - while (scan_swap_map_ssd_cluster_conflict(si, offset)) - scan_swap_map_try_ssd_cluster(si, &offset, &scan_base); + while (scan_swap_map_ssd_cluster_conflict(si, offset)) { + /* take a break if we already got some slots */ + if (n_ret) + goto done; + if (!scan_swap_map_try_ssd_cluster(si, &offset, + &scan_base)) + goto scan; + } } if (!(si->flags & SWP_WRITEOK)) goto no_page; @@ -650,7 +664,10 @@ checks: if (si->swap_map[offset]) { unlock_cluster(ci); - goto scan; + if (!n_ret) + goto scan; + else + goto done; } if (offset == si->lowest_bit) @@ -669,9 +686,43 @@ checks: inc_cluster_info_page(si, si->cluster_info, offset); unlock_cluster(ci); si->cluster_next = offset + 1; - si->flags -= SWP_SCANNING; + slots[n_ret++] = swp_entry(si->type, offset); - return offset; + /* got enough slots or reach max slots? */ + if ((n_ret == nr) || (offset >= si->highest_bit)) + goto done; + + /* search for next available slot */ + + /* time to take a break? */ + if (unlikely(--latency_ration < 0)) { + if (n_ret) + goto done; + spin_unlock(&si->lock); + cond_resched(); + spin_lock(&si->lock); + latency_ration = LATENCY_LIMIT; + } + + /* try to get more slots in cluster */ + if (si->cluster_info) { + if (scan_swap_map_try_ssd_cluster(si, &offset, &scan_base)) + goto checks; + else + goto done; + } + /* non-ssd case */ + ++offset; + + /* non-ssd case, still more slots in cluster? */ + if (si->cluster_nr && !si->swap_map[offset]) { + --si->cluster_nr; + goto checks; + } + +done: + si->flags -= SWP_SCANNING; + return n_ret; scan: spin_unlock(&si->lock); @@ -709,17 +760,41 @@ scan: no_page: si->flags -= SWP_SCANNING; - return 0; + return n_ret; } -swp_entry_t get_swap_page(void) +static unsigned long scan_swap_map(struct swap_info_struct *si, + unsigned char usage) +{ + swp_entry_t entry; + int n_ret; + + n_ret = scan_swap_map_slots(si, usage, 1, &entry); + + if (n_ret) + return swp_offset(entry); + else + return 0; + +} + +int get_swap_pages(int n_goal, swp_entry_t swp_entries[]) { struct swap_info_struct *si, *next; - pgoff_t offset; + long avail_pgs; + int n_ret = 0; - if (atomic_long_read(&nr_swap_pages) <= 0) + avail_pgs = atomic_long_read(&nr_swap_pages); + if (avail_pgs <= 0) goto noswap; - atomic_long_dec(&nr_swap_pages); + + if (n_goal > SWAP_BATCH) + n_goal = SWAP_BATCH; + + if (n_goal > avail_pgs) + n_goal = avail_pgs; + + atomic_long_sub(n_goal, &nr_swap_pages); spin_lock(&swap_avail_lock); @@ -745,14 +820,14 @@ start_over: spin_unlock(&si->lock); goto nextsi; } - - /* This is called for allocating swap entry for cache */ - offset = scan_swap_map(si, SWAP_HAS_CACHE); + n_ret = scan_swap_map_slots(si, SWAP_HAS_CACHE, + n_goal, swp_entries); spin_unlock(&si->lock); - if (offset) - return swp_entry(si->type, offset); + if (n_ret) + goto check_out; pr_debug("scan_swap_map of si %d failed to find offset\n", - si->type); + si->type); + spin_lock(&swap_avail_lock); nextsi: /* @@ -763,7 +838,8 @@ nextsi: * up between us dropping swap_avail_lock and taking si->lock. * Since we dropped the swap_avail_lock, the swap_avail_head * list may have been modified; so if next is still in the - * swap_avail_head list then try it, otherwise start over. + * swap_avail_head list then try it, otherwise start over + * if we have not gotten any slots. */ if (plist_node_empty(&next->avail_list)) goto start_over; @@ -771,9 +847,19 @@ nextsi: spin_unlock(&swap_avail_lock); - atomic_long_inc(&nr_swap_pages); +check_out: + if (n_ret < n_goal) + atomic_long_add((long) (n_goal-n_ret), &nr_swap_pages); noswap: - return (swp_entry_t) {0}; + return n_ret; +} + +swp_entry_t get_swap_page(void) +{ + swp_entry_t entry; + + get_swap_pages(1, &entry); + return entry; } /* The only caller of this function is now suspend routine */ _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
