[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>

1 files changed, 10 insertions, 0 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)