Re: [PATCH v3 2/3] resource: Add release_mem_region_adjustable()

[Andrew Morton]

On Wed, 10 Apr 2013 15:08:29 -0700 (PDT) David Rientjes <rient...@google.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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