linux-kernel - Re: [PATCH v3 2/3] resource: Add release_mem_region

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Date:	Wed, 10 Apr 2013 15:24:04 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Toshi Kani <toshi.kani@...com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, linuxram@...ibm.com,
	guz.fnst@...fujitsu.com, tmac@...com,
	isimatu.yasuaki@...fujitsu.com, wency@...fujitsu.com,
	tangchen@...fujitsu.com, jiang.liu@...wei.com
Subject: Re: [PATCH v3 2/3] resource: Add release_mem_region_adjustable()

On Wed, 10 Apr 2013 15:08:29 -0700 (PDT) David Rientjes <rientjes@...gle.com> wrote:

> On Wed, 10 Apr 2013, Toshi Kani wrote:
> 
> > > I'll switch it to GFP_ATOMIC.  Which is horridly lame but the
> > > allocation is small and alternatives are unobvious.
> > 
> > Great!  Again, thanks for the update!
> 
> release_mem_region_adjustable() allocates at most one struct resource, so 
> why not do kmalloc(sizeof(struct resource), GFP_KERNEL) before taking 
> resource_lock and then testing whether it's NULL or not when splitting?  
> It unnecessarily allocates memory when there's no split, but 
> __remove_pages() shouldn't be a hotpath.

yup.

--- a/kernel/resource.c~resource-add-release_mem_region_adjustable-fix-fix
+++ a/kernel/resource.c
@@ -1046,7 +1046,8 @@ int release_mem_region_adjustable(struct
 			resource_size_t start, resource_size_t size)
 {
 	struct resource **p;
-	struct resource *res, *new;
+	struct resource *res;
+	struct resource *new_res;
 	resource_size_t end;
 	int ret = -EINVAL;
 
@@ -1054,6 +1055,9 @@ int release_mem_region_adjustable(struct
 	if ((start < parent->start) || (end > parent->end))
 		return ret;
 
+	/* The kzalloc() result gets checked later */
+	new_res = kzalloc(sizeof(struct resource), GFP_KERNEL);
+
 	p = &parent->child;
 	write_lock(&resource_lock);
 
@@ -1091,32 +1095,33 @@ int release_mem_region_adjustable(struct
 						start - res->start);
 		} else {
 			/* split into two entries */
-			new = kzalloc(sizeof(struct resource), GFP_ATOMIC);
-			if (!new) {
+			if (!new_res) {
 				ret = -ENOMEM;
 				break;
 			}
-			new->name = res->name;
-			new->start = end + 1;
-			new->end = res->end;
-			new->flags = res->flags;
-			new->parent = res->parent;
-			new->sibling = res->sibling;
-			new->child = NULL;
+			new_res->name = res->name;
+			new_res->start = end + 1;
+			new_res->end = res->end;
+			new_res->flags = res->flags;
+			new_res->parent = res->parent;
+			new_res->sibling = res->sibling;
+			new_res->child = NULL;
 
 			ret = __adjust_resource(res, res->start,
 						start - res->start);
 			if (ret) {
-				kfree(new);
+				kfree(new_res);
 				break;
 			}
-			res->sibling = new;
+			res->sibling = new_res;
+			new_res = NULL;
 		}
 
 		break;
 	}
 
 	write_unlock(&resource_lock);
+	kfree(new_res);
 	return ret;
 }
 #endif	/* CONFIG_MEMORY_HOTPLUG */
_

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