[JFFS2] Trigger garbage collection when very_dirty_list size becomes excessive

With huge amounts of free space, we weren't bothering to GC for while a
while, and pathological numbers of obsolete nodes were accumulating,
seriously affecting performance on NAND flash (OLPC trac #3978)

Signed-off-by: David Woodhouse <dwmw2@infradead.org>

3 files changed, 24 insertions, 2 deletions

diff --git a/fs/jffs2/build.c b/fs/jffs2/build.c
index 0ca2fff2617f..8c27c12816ba 100644
--- a/fs/jffs2/build.c
+++ b/fs/jffs2/build.c
@@ -285,6 +285,14 @@ static void jffs2_calc_trigger_levels(struct jffs2_sb_info *c)
            than actually making progress? */
         c->resv_blocks_gcbad = 0;//c->resv_blocks_deletion + 2;
 
+        /* What number of 'very dirty' eraseblocks do we allow before we
+           trigger the GC thread even if we don't _need_ the space. When we
+           can't mark nodes obsolete on the medium, the old dirty nodes cause
+           performance problems because we have to inspect and discard them. */
+        c->vdirty_blocks_gctrigger = c->resv_blocks_gcmerge;
+        if (jffs2_can_mark_obsolete(c))
+                c->vdirty_blocks_gctrigger *= 10;
+
         /* If there's less than this amount of dirty space, don't bother
            trying to GC to make more space. It'll be a fruitless task */
         c->nospc_dirty_size = c->sector_size + (c->flash_size / 100);
@@ -303,6 +311,8 @@ static void jffs2_calc_trigger_levels(struct jffs2_sb_info *c)
                   c->resv_blocks_gcbad, c->resv_blocks_gcbad*c->sector_size/1024);
         dbg_fsbuild("Amount of dirty space required to GC: %d bytes\n",
                   c->nospc_dirty_size);
+        dbg_fsbuild("Very dirty blocks before GC triggered: %d\n",
+                  c->vdirty_blocks_gctrigger);
 }
 
 int jffs2_do_mount_fs(struct jffs2_sb_info *c)
diff --git a/fs/jffs2/jffs2_fs_sb.h b/fs/jffs2/jffs2_fs_sb.h
index ae99cd7fd43b..3a2197f3c812 100644
--- a/fs/jffs2/jffs2_fs_sb.h
+++ b/fs/jffs2/jffs2_fs_sb.h
@@ -69,6 +69,8 @@ struct jffs2_sb_info {
         uint8_t resv_blocks_gctrigger;  /* ... wake up the GC thread */
         uint8_t resv_blocks_gcbad;      /* ... pick a block from the bad_list to GC */
         uint8_t resv_blocks_gcmerge;    /* ... merge pages when garbage collecting */
+        /* Number of 'very dirty' blocks before we trigger immediate GC */
+        uint8_t vdirty_blocks_gctrigger;
 
         uint32_t nospc_dirty_size;
 
diff --git a/fs/jffs2/nodemgmt.c b/fs/jffs2/nodemgmt.c
index 5b49bff364b4..1b79534e9d48 100644
--- a/fs/jffs2/nodemgmt.c
+++ b/fs/jffs2/nodemgmt.c
@@ -722,6 +722,8 @@ int jffs2_thread_should_wake(struct jffs2_sb_info *c)
 {
         int ret = 0;
         uint32_t dirty;
+        int nr_very_dirty = 0;
+        struct jffs2_eraseblock *jeb;
 
         if (c->unchecked_size) {
                 D1(printk(KERN_DEBUG "jffs2_thread_should_wake(): unchecked_size %d, checked_ino #%d\n",
@@ -743,8 +745,16 @@ int jffs2_thread_should_wake(struct jffs2_sb_info *c)
                         (dirty > c->nospc_dirty_size))
                 ret = 1;
 
-        D1(printk(KERN_DEBUG "jffs2_thread_should_wake(): nr_free_blocks %d, nr_erasing_blocks %d, dirty_size 0x%x: %s\n",
-                  c->nr_free_blocks, c->nr_erasing_blocks, c->dirty_size, ret?"yes":"no"));
+        list_for_each_entry(jeb, &c->very_dirty_list, list) {
+                nr_very_dirty++;
+                if (nr_very_dirty == c->vdirty_blocks_gctrigger) {
+                        ret = 1;
+                        D1(break);
+                }
+        }
+
+        D1(printk(KERN_DEBUG "jffs2_thread_should_wake(): nr_free_blocks %d, nr_erasing_blocks %d, dirty_size 0x%x, vdirty_blocks %d: %s\n",
+                  c->nr_free_blocks, c->nr_erasing_blocks, c->dirty_size, nr_very_dirty, ret?"yes":"no"));
 
         return ret;
 }