Gitweb:     
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=f1a9ee758de7de1e040de849fdef46e6802ea117
Commit:     f1a9ee758de7de1e040de849fdef46e6802ea117
Parent:     fef1bdd68c81b71882ccb6f47c70980a03182063
Author:     Rik van Riel <[EMAIL PROTECTED]>
AuthorDate: Thu Feb 7 00:14:08 2008 -0800
Committer:  Linus Torvalds <[EMAIL PROTECTED]>
CommitDate: Thu Feb 7 08:42:19 2008 -0800

    kswapd should only wait on IO if there is IO
    
    The current kswapd (and try_to_free_pages) code has an oddity where the
    code will wait on IO, even if there is no IO in flight.  This problem is
    notable especially when the system scans through many unfreeable pages,
    causing unnecessary stalls in the VM.
    
    Additionally, tasks without __GFP_FS or __GFP_IO in the direct reclaim path
    will sleep if a significant number of pages are encountered that should be
    written out.  This gives kswapd a chance to write out those pages, while
    the direct reclaim task sleeps.
    
    Signed-off-by: Rik van Riel <[EMAIL PROTECTED]>
    Signed-off-by: Andrew Morton <[EMAIL PROTECTED]>
    Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
---
 mm/vmscan.c |   27 ++++++++++++++++++++++-----
 1 files changed, 22 insertions(+), 5 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index b7d868c..1b85217 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -70,6 +70,13 @@ struct scan_control {
 
        int order;
 
+       /*
+        * Pages that have (or should have) IO pending.  If we run into
+        * a lot of these, we're better off waiting a little for IO to
+        * finish rather than scanning more pages in the VM.
+        */
+       int nr_io_pages;
+
        /* Which cgroup do we reclaim from */
        struct mem_cgroup *mem_cgroup;
 
@@ -499,8 +506,10 @@ static unsigned long shrink_page_list(struct list_head 
*page_list,
                         */
                        if (sync_writeback == PAGEOUT_IO_SYNC && may_enter_fs)
                                wait_on_page_writeback(page);
-                       else
+                       else {
+                               sc->nr_io_pages++;
                                goto keep_locked;
+                       }
                }
 
                referenced = page_referenced(page, 1, sc->mem_cgroup);
@@ -539,8 +548,10 @@ static unsigned long shrink_page_list(struct list_head 
*page_list,
                if (PageDirty(page)) {
                        if (sc->order <= PAGE_ALLOC_COSTLY_ORDER && referenced)
                                goto keep_locked;
-                       if (!may_enter_fs)
+                       if (!may_enter_fs) {
+                               sc->nr_io_pages++;
                                goto keep_locked;
+                       }
                        if (!sc->may_writepage)
                                goto keep_locked;
 
@@ -551,8 +562,10 @@ static unsigned long shrink_page_list(struct list_head 
*page_list,
                        case PAGE_ACTIVATE:
                                goto activate_locked;
                        case PAGE_SUCCESS:
-                               if (PageWriteback(page) || PageDirty(page))
+                               if (PageWriteback(page) || PageDirty(page)) {
+                                       sc->nr_io_pages++;
                                        goto keep;
+                               }
                                /*
                                 * A synchronous write - probably a ramdisk.  Go
                                 * ahead and try to reclaim the page.
@@ -1259,6 +1272,7 @@ static unsigned long do_try_to_free_pages(struct zone 
**zones, gfp_t gfp_mask,
 
        for (priority = DEF_PRIORITY; priority >= 0; priority--) {
                sc->nr_scanned = 0;
+               sc->nr_io_pages = 0;
                if (!priority)
                        disable_swap_token();
                nr_reclaimed += shrink_zones(priority, zones, sc);
@@ -1292,7 +1306,8 @@ static unsigned long do_try_to_free_pages(struct zone 
**zones, gfp_t gfp_mask,
                }
 
                /* Take a nap, wait for some writeback to complete */
-               if (sc->nr_scanned && priority < DEF_PRIORITY - 2)
+               if (sc->nr_scanned && priority < DEF_PRIORITY - 2 &&
+                               sc->nr_io_pages > sc->swap_cluster_max)
                        congestion_wait(WRITE, HZ/10);
        }
        /* top priority shrink_caches still had more to do? don't OOM, then */
@@ -1424,6 +1439,7 @@ loop_again:
                if (!priority)
                        disable_swap_token();
 
+               sc.nr_io_pages = 0;
                all_zones_ok = 1;
 
                /*
@@ -1516,7 +1532,8 @@ loop_again:
                 * OK, kswapd is getting into trouble.  Take a nap, then take
                 * another pass across the zones.
                 */
-               if (total_scanned && priority < DEF_PRIORITY - 2)
+               if (total_scanned && priority < DEF_PRIORITY - 2 &&
+                                       sc.nr_io_pages > sc.swap_cluster_max)
                        congestion_wait(WRITE, HZ/10);
 
                /*
-
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