kernel - Fix memory starvation issue w/tmpfs

* TMPFS relies on the pagedaemon to retire dirty pages to swap.  The normal
  buffer cache flushing won't do the job (nor do we want it to).  To avoid
  starving the system we change bio_page_alloc() to not dig into the
  system reserve when allocating pages for TMPFS.

Reported-by: tuxillo (Antonio Huete)

diff --git a/sys/kern/vfs_bio.c b/sys/kern/vfs_bio.c
index f880bb4..3c2e1e2 100644 (file)
--- a/sys/kern/vfs_bio.c
+++ b/sys/kern/vfs_bio.c
@@ -102,7 +102,8 @@ static void vfs_dirty_one_page(struct buf *bp, int pageno, vm_page_t m);
 #endif
 static void vfs_vmio_release(struct buf *bp);
 static int flushbufqueues(struct buf *marker, bufq_type_t q);
-static vm_page_t bio_page_alloc(vm_object_t obj, vm_pindex_t pg, int deficit);
+static vm_page_t bio_page_alloc(struct buf *bp, vm_object_t obj,
+                               vm_pindex_t pg, int deficit);
 
 static void bd_signal(long totalspace);
 static void buf_daemon(void);
@@ -3389,7 +3390,7 @@ allocbuf(struct buf *bp, int size)
                                         * with paging I/O, no matter which
                                         * process we are.
                                         */
-                                       m = bio_page_alloc(obj, pi, desiredpages - bp->b_xio.xio_npages);
+                                       m = bio_page_alloc(bp, obj, pi, desiredpages - bp->b_xio.xio_npages);
                                        if (m) {
                                                vm_page_wire(m);
                                                vm_page_flag_clear(m, PG_ZERO);
@@ -4483,7 +4484,7 @@ vm_hold_load_pages(struct buf *bp, vm_offset_t from, vm_offset_t to)
                 * process we are.
                 */
                vm_object_hold(&kernel_object);
-               p = bio_page_alloc(&kernel_object, pg >> PAGE_SHIFT,
+               p = bio_page_alloc(bp, &kernel_object, pg >> PAGE_SHIFT,
                                   (vm_pindex_t)((to - pg) >> PAGE_SHIFT));
                vm_object_drop(&kernel_object);
                if (p) {
@@ -4511,10 +4512,16 @@ vm_hold_load_pages(struct buf *bp, vm_offset_t from, vm_offset_t to)
  *      function will use the system reserve with the hope that the page
  *      allocations can be returned to PQ_CACHE/PQ_FREE when the caller
  *      is done with the buffer.
+ *
+ * NOTE! However, TMPFS is a special case because flushing a dirty buffer
+ *      to TMPFS doesn't clean the page.  For TMPFS, only the pagedaemon
+ *      is capable of retiring pages (to swap).  For TMPFS we don't dig
+ *      into the system reserve because doing so could stall out pretty
+ *      much every process running on the system.
  */
 static
 vm_page_t
-bio_page_alloc(vm_object_t obj, vm_pindex_t pg, int deficit)
+bio_page_alloc(struct buf *bp, vm_object_t obj, vm_pindex_t pg, int deficit)
 {
        int vmflags = VM_ALLOC_NORMAL | VM_ALLOC_NULL_OK;
        vm_page_t p;
@@ -4541,6 +4548,8 @@ bio_page_alloc(vm_object_t obj, vm_pindex_t pg, int deficit)
         */
        if (curthread->td_flags & TDF_SYSTHREAD)
                vmflags |= VM_ALLOC_SYSTEM | VM_ALLOC_INTERRUPT;
+       else if (bp->b_vp && bp->b_vp->v_tag == VT_TMPFS)
+               vmflags |= 0;
        else
                vmflags |= VM_ALLOC_SYSTEM;