The patch titled
Subject: mm/vmalloc: add more comments to the adjust_va_to_fit_type()
has been added to the -mm tree. Its filename is
mm-vmalloc-add-more-comments-to-the-adjust_va_to_fit_type.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-vmalloc-add-more-comments-to-the-adjust_va_to_fit_type.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-vmalloc-add-more-comments-to-the-adjust_va_to_fit_type.patch
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------------------------------------------------------
From: "Uladzislau Rezki (Sony)" <urezki@xxxxxxxxx>
Subject: 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.
Link: http://lkml.kernel.org/r/20191016095438.12391-3-urezki@xxxxxxxxx
Signed-off-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: Daniel Wagner <dwagner@xxxxxxx>
Cc: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Uladzislau Rezki <urezki@xxxxxxxxx>
Cc: Hillf Danton <hdanton@xxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Oleksiy Avramchenko <oleksiy.avramchenko@xxxxxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/vmalloc.c | 13 +++++++++++++
1 file changed, 13 insertions(+)
--- a/mm/vmalloc.c~mm-vmalloc-add-more-comments-to-the-adjust_va_to_fit_type
+++ a/mm/vmalloc.c
@@ -968,6 +968,19 @@ adjust_va_to_fit_type(struct vmap_area *
* 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)
_
Patches currently in -mm which might be from urezki@xxxxxxxxx are
mm-vmalloc-remove-preempt_disable-enable-when-do-preloading.patch
mm-vmalloc-respect-passed-gfp_mask-when-do-preloading.patch
mm-vmalloc-add-more-comments-to-the-adjust_va_to_fit_type.patch
