From 03fdc1d58204092a2d0b25b5353833fc8d3e9a9f Mon Sep 17 00:00:00 2001
From: "Uladzislau Rezki (Sony)" <urezki@gmail.com>
Date: Sat, 30 Nov 2019 17:54:40 -0800
Subject: [PATCH] mm/vmalloc: add more comments to the adjust_va_to_fit_type()
References: bnc#1155780 (VM/FS functional and performance backports)
Patch-mainline: v5.5-rc1
Git-commit: 060650a2a0598d61bac6ce64578b176cb0e18b06
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@gmail.com
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Daniel Wagner <dwagner@suse.de>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Uladzislau Rezki <urezki@gmail.com>
Cc: Hillf Danton <hdanton@sina.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Oleksiy Avramchenko <oleksiy.avramchenko@sonymobile.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Mel Gorman <mgorman@suse.de>
---
mm/vmalloc.c | 13 +++++++++++++
1 file changed, 13 insertions(+)
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 54cb5942468c..abcf28f715b9 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -971,6 +971,19 @@ 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)