percpu: move region iterations out of pcpu_[de]populate_chunk()

Previously, pcpu_[de]populate_chunk() were called with the range which
may contain multiple target regions in it and
pcpu_[de]populate_chunk() iterated over the regions.  This has the
benefit of batching up cache flushes for all the regions; however,
we're planning to add more bookkeeping logic around [de]population to
support atomic allocations and this delegation of iterations gets in
the way.

This patch moves the region iterations out of
pcpu_[de]populate_chunk() into its callers - pcpu_alloc() and
pcpu_reclaim() - so that we can later add logic to track more states
around them.  This change may make cache and tlb flushes more frequent
but multi-region [de]populations are rare anyway and if this actually
becomes a problem, it's not difficult to factor out cache flushes as
separate callbacks which are directly invoked from percpu.c.

Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 16 insertions, 41 deletions

diff --git a/mm/percpu-vm.c b/mm/percpu-vm.c
index edf709793318..538998a137d2 100644
--- a/mm/percpu-vm.c
+++ b/mm/percpu-vm.c
@@ -261,8 +261,8 @@ static void pcpu_post_map_flush(struct pcpu_chunk *chunk,
 /**
  * pcpu_populate_chunk - populate and map an area of a pcpu_chunk
  * @chunk: chunk of interest
- * @off: offset to the area to populate
- * @size: size of the area to populate in bytes
+ * @page_start: the start page
+ * @page_end: the end page
  *
  * For each cpu, populate and map pages [@page_start,@page_end) into
  * @chunk.
@@ -270,66 +270,43 @@ static void pcpu_post_map_flush(struct pcpu_chunk *chunk,
  * CONTEXT:
  * pcpu_alloc_mutex, does GFP_KERNEL allocation.
  */
-static int pcpu_populate_chunk(struct pcpu_chunk *chunk, int off, int size)
+static int pcpu_populate_chunk(struct pcpu_chunk *chunk,
+                               int page_start, int page_end)
 {
-        int page_start = PFN_DOWN(off);
-        int page_end = PFN_UP(off + size);
-        int free_end = page_start, unmap_end = page_start;
         struct page **pages;
-        int rs, re, rc;
 
         pages = pcpu_get_pages(chunk);
         if (!pages)
                 return -ENOMEM;
 
-        /* alloc and map */
-        pcpu_for_each_unpop_region(chunk, rs, re, page_start, page_end) {
-                rc = pcpu_alloc_pages(chunk, pages, rs, re);
-                if (rc)
-                        goto err_free;
-                free_end = re;
-        }
+        if (pcpu_alloc_pages(chunk, pages, page_start, page_end))
+                return -ENOMEM;
 
-        pcpu_for_each_unpop_region(chunk, rs, re, page_start, page_end) {
-                rc = pcpu_map_pages(chunk, pages, rs, re);
-                if (rc)
-                        goto err_unmap;
-                unmap_end = re;
+        if (pcpu_map_pages(chunk, pages, page_start, page_end)) {
+                pcpu_free_pages(chunk, pages, page_start, page_end);
+                return -ENOMEM;
         }
         pcpu_post_map_flush(chunk, page_start, page_end);
 
         return 0;
-
-err_unmap:
-        pcpu_pre_unmap_flush(chunk, page_start, unmap_end);
-        pcpu_for_each_unpop_region(chunk, rs, re, page_start, unmap_end)
-                pcpu_unmap_pages(chunk, pages, rs, re);
-        pcpu_post_unmap_tlb_flush(chunk, page_start, unmap_end);
-err_free:
-        pcpu_for_each_unpop_region(chunk, rs, re, page_start, free_end)
-                pcpu_free_pages(chunk, pages, rs, re);
-        return rc;
 }
 
 /**
  * pcpu_depopulate_chunk - depopulate and unmap an area of a pcpu_chunk
  * @chunk: chunk to depopulate
- * @off: offset to the area to depopulate
- * @size: size of the area to depopulate in bytes
+ * @page_start: the start page
+ * @page_end: the end page
  *
  * For each cpu, depopulate and unmap pages [@page_start,@page_end)
- * from @chunk.  If @flush is true, vcache is flushed before unmapping
- * and tlb after.
+ * from @chunk.
  *
  * CONTEXT:
  * pcpu_alloc_mutex.
  */
-static void pcpu_depopulate_chunk(struct pcpu_chunk *chunk, int off, int size)
+static void pcpu_depopulate_chunk(struct pcpu_chunk *chunk,
+                                  int page_start, int page_end)
 {
-        int page_start = PFN_DOWN(off);
-        int page_end = PFN_UP(off + size);
         struct page **pages;
-        int rs, re;
 
         /*
          * If control reaches here, there must have been at least one
@@ -342,13 +319,11 @@ static void pcpu_depopulate_chunk(struct pcpu_chunk *chunk, int off, int size)
         /* unmap and free */
         pcpu_pre_unmap_flush(chunk, page_start, page_end);
 
-        pcpu_for_each_pop_region(chunk, rs, re, page_start, page_end)
-                pcpu_unmap_pages(chunk, pages, rs, re);
+        pcpu_unmap_pages(chunk, pages, page_start, page_end);
 
         /* no need to flush tlb, vmalloc will handle it lazily */
 
-        pcpu_for_each_pop_region(chunk, rs, re, page_start, page_end)
-                pcpu_free_pages(chunk, pages, rs, re);
+        pcpu_free_pages(chunk, pages, page_start, page_end);
 }
 
 static struct pcpu_chunk *pcpu_create_chunk(void)