[PATCH] Swap Migration V5: PF_SWAPWRITE to allow writing to swap

Add PF_SWAPWRITE to control a processes permission to write to swap.

- Use PF_SWAPWRITE in may_write_to_queue() instead of checking for kswapd
  and pdflush

- Set PF_SWAPWRITE flag for kswapd and pdflush

Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

3 files changed, 4 insertions, 5 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 7da33619d5d0..a74662077d60 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -895,6 +895,7 @@ do { if (atomic_dec_and_test(&(tsk)->usage)) __put_task_struct(tsk); } while(0)
 #define PF_SYNCWRITE    0x00200000      /* I am doing a sync write */
 #define PF_BORROWED_MM  0x00400000      /* I am a kthread doing use_mm */
 #define PF_RANDOMIZE    0x00800000      /* randomize virtual address space */
+#define PF_SWAPWRITE    0x01000000      /* Allowed to write to swap */
 
 /*
  * Only the _current_ task can read/write to tsk->flags, but other
diff --git a/mm/pdflush.c b/mm/pdflush.c
index 52822c98c489..c4b6d0afd736 100644
--- a/mm/pdflush.c
+++ b/mm/pdflush.c
@@ -90,7 +90,7 @@ struct pdflush_work {
 
 static int __pdflush(struct pdflush_work *my_work)
 {
-        current->flags |= PF_FLUSHER;
+        current->flags |= PF_FLUSHER | PF_SWAPWRITE;
         my_work->fn = NULL;
         my_work->who = current;
         INIT_LIST_HEAD(&my_work->list);
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 261a56ee11b6..6c30a8c59795 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -268,9 +268,7 @@ static inline int is_page_cache_freeable(struct page *page)
 
 static int may_write_to_queue(struct backing_dev_info *bdi)
 {
-        if (current_is_kswapd())
-                return 1;
-        if (current_is_pdflush())       /* This is unlikely, but why not... */
+        if (current->flags & PF_SWAPWRITE)
                 return 1;
         if (!bdi_write_congested(bdi))
                 return 1;
@@ -1299,7 +1297,7 @@ static int kswapd(void *p)
          * us from recursively trying to free more memory as we're
          * trying to free the first piece of memory in the first place).
          */
-        tsk->flags |= PF_MEMALLOC|PF_KSWAPD;
+        tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
 
         order = 0;
         for ( ; ; ) {