[lkml]   [2019]   [Oct]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
Patch in this message
Subject[PATCH v3 3/3] mm/vmalloc: add more comments to the adjust_va_to_fit_type()
When fit type is NE_FIT_TYPE there is a need in one extra object.
Usually the "ne_fit_preload_node" per-CPU variable has it and
there is no need in GFP_NOWAIT allocation, but there are exceptions.

This commit just adds more explanations, as a result giving
answers on questions like when it can occur, how often, under
which conditions and what happens if GFP_NOWAIT gets failed.

Signed-off-by: Uladzislau Rezki (Sony) <>
mm/vmalloc.c | 13 +++++++++++++
1 file changed, 13 insertions(+)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 593bf554518d..2290a0d270e4 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -969,6 +969,19 @@ adjust_va_to_fit_type(struct vmap_area *va,
* There are a few exceptions though, as an example it is
* a first allocation (early boot up) when we have "one"
* big free space that has to be split.
+ *
+ * Also we can hit this path in case of regular "vmap"
+ * allocations, if "this" current CPU was not preloaded.
+ * See the comment in alloc_vmap_area() why. If so, then
+ * GFP_NOWAIT is used instead to get an extra object for
+ * split purpose. That is rare and most time does not
+ * occur.
+ *
+ * What happens if an allocation gets failed. Basically,
+ * an "overflow" path is triggered to purge lazily freed
+ * areas to free some memory, then, the "retry" path is
+ * triggered to repeat one more time. See more details
+ * in alloc_vmap_area() function.
lva = kmem_cache_alloc(vmap_area_cachep, GFP_NOWAIT);
if (!lva)
 \ /
  Last update: 2019-10-16 11:55    [W:0.082 / U:1.840 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site