percpu: make pcpu_alloc_area() capable of allocating only from populated areas
Update pcpu_alloc_area() so that it can skip unpopulated areas if the
new parameter @pop_only is true. This is implemented by a new
function, pcpu_fit_in_area(), which determines the amount of head
padding considering the alignment and populated state.
@pop_only is currently always false but this will be used to implement
atomic allocation.
Signed-off-by: Tejun Heo <tj@kernel.org>
diff --git a/mm/percpu.c b/mm/percpu.c
index e59f7b4..e18aa14 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -400,10 +400,60 @@
}
/**
+ * pcpu_fit_in_area - try to fit the requested allocation in a candidate area
+ * @chunk: chunk the candidate area belongs to
+ * @off: the offset to the start of the candidate area
+ * @this_size: the size of the candidate area
+ * @size: the size of the target allocation
+ * @align: the alignment of the target allocation
+ * @pop_only: only allocate from already populated region
+ *
+ * We're trying to allocate @size bytes aligned at @align. @chunk's area
+ * at @off sized @this_size is a candidate. This function determines
+ * whether the target allocation fits in the candidate area and returns the
+ * number of bytes to pad after @off. If the target area doesn't fit, -1
+ * is returned.
+ *
+ * If @pop_only is %true, this function only considers the already
+ * populated part of the candidate area.
+ */
+static int pcpu_fit_in_area(struct pcpu_chunk *chunk, int off, int this_size,
+ int size, int align, bool pop_only)
+{
+ int cand_off = off;
+
+ while (true) {
+ int head = ALIGN(cand_off, align) - off;
+ int page_start, page_end, rs, re;
+
+ if (this_size < head + size)
+ return -1;
+
+ if (!pop_only)
+ return head;
+
+ /*
+ * If the first unpopulated page is beyond the end of the
+ * allocation, the whole allocation is populated;
+ * otherwise, retry from the end of the unpopulated area.
+ */
+ page_start = PFN_DOWN(head + off);
+ page_end = PFN_UP(head + off + size);
+
+ rs = page_start;
+ pcpu_next_unpop(chunk, &rs, &re, PFN_UP(off + this_size));
+ if (rs >= page_end)
+ return head;
+ cand_off = re * PAGE_SIZE;
+ }
+}
+
+/**
* pcpu_alloc_area - allocate area from a pcpu_chunk
* @chunk: chunk of interest
* @size: wanted size in bytes
* @align: wanted align
+ * @pop_only: allocate only from the populated area
*
* Try to allocate @size bytes area aligned at @align from @chunk.
* Note that this function only allocates the offset. It doesn't
@@ -418,7 +468,8 @@
* Allocated offset in @chunk on success, -1 if no matching area is
* found.
*/
-static int pcpu_alloc_area(struct pcpu_chunk *chunk, int size, int align)
+static int pcpu_alloc_area(struct pcpu_chunk *chunk, int size, int align,
+ bool pop_only)
{
int oslot = pcpu_chunk_slot(chunk);
int max_contig = 0;
@@ -434,11 +485,11 @@
if (off & 1)
continue;
- /* extra for alignment requirement */
- head = ALIGN(off, align) - off;
-
this_size = (p[1] & ~1) - off;
- if (this_size < head + size) {
+
+ head = pcpu_fit_in_area(chunk, off, this_size, size, align,
+ pop_only);
+ if (head < 0) {
if (!seen_free) {
chunk->first_free = i;
seen_free = true;
@@ -730,7 +781,7 @@
spin_lock_irqsave(&pcpu_lock, flags);
}
- off = pcpu_alloc_area(chunk, size, align);
+ off = pcpu_alloc_area(chunk, size, align, false);
if (off >= 0)
goto area_found;
@@ -761,7 +812,7 @@
goto restart;
}
- off = pcpu_alloc_area(chunk, size, align);
+ off = pcpu_alloc_area(chunk, size, align, false);
if (off >= 0)
goto area_found;
}