[PATCH] mm, hugetlb: move the error handle logic out of normal code path

[PATCH] mm, hugetlb: move the error handle logic out of normal code path

[Jianyu Zhan]

alloc_huge_page() now mixes normal code path with error handle logic.
This patches move out the error handle logic, to make normal code
path more clean and redue code duplicate.

Signed-off-by: Jianyu Zhan <nasa4836@gmail.com>
---
 mm/hugetlb.c | 26 +++++++++++++-------------
 1 file changed, 13 insertions(+), 13 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 26b1464..e81c69e 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1246,24 +1246,17 @@ static struct page *alloc_huge_page(struct vm_area_struct *vma,
 			return ERR_PTR(-ENOSPC);
 
 	ret = hugetlb_cgroup_charge_cgroup(idx, pages_per_huge_page(h), &h_cg);
-	if (ret) {
-		if (chg || avoid_reserve)
-			hugepage_subpool_put_pages(spool, 1);
-		return ERR_PTR(-ENOSPC);
-	}
+	if (ret)
+		goto out_subpool_put;
+
 	spin_lock(&hugetlb_lock);
 	page = dequeue_huge_page_vma(h, vma, addr, avoid_reserve, chg);
 	if (!page) {
 		spin_unlock(&hugetlb_lock);
 		page = alloc_buddy_huge_page(h, NUMA_NO_NODE);
-		if (!page) {
-			hugetlb_cgroup_uncharge_cgroup(idx,
-						       pages_per_huge_page(h),
-						       h_cg);
-			if (chg || avoid_reserve)
-				hugepage_subpool_put_pages(spool, 1);
-			return ERR_PTR(-ENOSPC);
-		}
+		if (!page)
+			goto out_uncharge_cgroup;
+
 		spin_lock(&hugetlb_lock);
 		list_move(&page->lru, &h->hugepage_activelist);
 		/* Fall through */
@@ -1275,6 +1268,13 @@ static struct page *alloc_huge_page(struct vm_area_struct *vma,
 
 	vma_commit_reservation(h, vma, addr);
 	return page;
+
+out_uncharge_cgroup:
+	hugetlb_cgroup_uncharge_cgroup(idx, pages_per_huge_page(h), h_cg);
+out_subpool_put:
+	if (chg || avoid_reserve)
+		hugepage_subpool_put_pages(spool, 1);
+	return ERR_PTR(-ENOSPC);
 }
 
 /*
-- 
2.0.0-rc3

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Re: [PATCH] mm, hugetlb: move the error handle logic out of normal code path

[Michal Hocko]

On Wed 14-05-14 15:10:59, Jianyu Zhan wrote:
> alloc_huge_page() now mixes normal code path with error handle logic.
> This patches move out the error handle logic, to make normal code
> path more clean and redue code duplicate.

I don't know. Part of the function returns and cleans up on its own and
other part relies on clean up labels. This is not so much nicer than the
previous state.

> Signed-off-by: Jianyu Zhan <nasa4836@gmail.com>
> ---
>  mm/hugetlb.c | 26 +++++++++++++-------------
>  1 file changed, 13 insertions(+), 13 deletions(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 26b1464..e81c69e 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1246,24 +1246,17 @@ static struct page *alloc_huge_page(struct vm_area_struct *vma,
>  			return ERR_PTR(-ENOSPC);
>  
>  	ret = hugetlb_cgroup_charge_cgroup(idx, pages_per_huge_page(h), &h_cg);
> -	if (ret) {
> -		if (chg || avoid_reserve)
> -			hugepage_subpool_put_pages(spool, 1);
> -		return ERR_PTR(-ENOSPC);
> -	}
> +	if (ret)
> +		goto out_subpool_put;
> +
>  	spin_lock(&hugetlb_lock);
>  	page = dequeue_huge_page_vma(h, vma, addr, avoid_reserve, chg);
>  	if (!page) {
>  		spin_unlock(&hugetlb_lock);
>  		page = alloc_buddy_huge_page(h, NUMA_NO_NODE);
> -		if (!page) {
> -			hugetlb_cgroup_uncharge_cgroup(idx,
> -						       pages_per_huge_page(h),
> -						       h_cg);
> -			if (chg || avoid_reserve)
> -				hugepage_subpool_put_pages(spool, 1);
> -			return ERR_PTR(-ENOSPC);
> -		}
> +		if (!page)
> +			goto out_uncharge_cgroup;
> +
>  		spin_lock(&hugetlb_lock);
>  		list_move(&page->lru, &h->hugepage_activelist);
>  		/* Fall through */
> @@ -1275,6 +1268,13 @@ static struct page *alloc_huge_page(struct vm_area_struct *vma,
>  
>  	vma_commit_reservation(h, vma, addr);
>  	return page;
> +
> +out_uncharge_cgroup:
> +	hugetlb_cgroup_uncharge_cgroup(idx, pages_per_huge_page(h), h_cg);
> +out_subpool_put:
> +	if (chg || avoid_reserve)
> +		hugepage_subpool_put_pages(spool, 1);
> +	return ERR_PTR(-ENOSPC);
>  }
>  
>  /*
> -- 
> 2.0.0-rc3
> 

-- 
Michal Hocko
SUSE Labs

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Re: [PATCH] mm, hugetlb: move the error handle logic out of normal code path

[Andrew Morton]

On Thu, 15 May 2014 11:01:42 +0200 Michal Hocko <mhocko@suse.cz> wrote:

> On Wed 14-05-14 15:10:59, Jianyu Zhan wrote:
> > alloc_huge_page() now mixes normal code path with error handle logic.
> > This patches move out the error handle logic, to make normal code
> > path more clean and redue code duplicate.
> 
> I don't know. Part of the function returns and cleans up on its own and
> other part relies on clean up labels. This is not so much nicer than the
> previous state.

That's actually a common pattern:

foo()
{
	if (check which doesn't change any state)
		return -Efoo;
	if (another check which doesn't change any state)
		return -Ebar;

	do_something_which_changes_state()
	
	if (another check)
		goto undo_that_state_chage;
	...

undo_that_state_change:
	...
}


This ties into the main reason why we use all these gotos: to support
evolution of the code.  With multiple return points we risk later
adding resource leaks and locking errors.  Plus the code becomes more
and more duplicative and spaghettified.


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Re: [PATCH] mm, hugetlb: move the error handle logic out of normal code path

[Michal Hocko]

On Thu 15-05-14 15:36:20, Andrew Morton wrote:
> On Thu, 15 May 2014 11:01:42 +0200 Michal Hocko <mhocko@suse.cz> wrote:
> 
> > On Wed 14-05-14 15:10:59, Jianyu Zhan wrote:
> > > alloc_huge_page() now mixes normal code path with error handle logic.
> > > This patches move out the error handle logic, to make normal code
> > > path more clean and redue code duplicate.
> > 
> > I don't know. Part of the function returns and cleans up on its own and
> > other part relies on clean up labels. This is not so much nicer than the
> > previous state.
> 
> That's actually a common pattern:
> 
> foo()
> {
> 	if (check which doesn't change any state)
> 		return -Efoo;
> 	if (another check which doesn't change any state)
> 		return -Ebar;
> 
> 	do_something_which_changes_state()
> 	
> 	if (another check)
> 		goto undo_that_state_chage;
> 	...
> 
> undo_that_state_change:
> 	...
> }

Right. I have misread the previous vma_needs_reservation and
hugepage_subpool_get_pages error path and already considered it as a
changing state one. Sorry about the confusion.
-- 
Michal Hocko
SUSE Labs

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Re: [PATCH] mm, hugetlb: move the error handle logic out of normal code path

[Davidlohr Bueso]

On Wed, 2014-05-14 at 15:10 +0800, Jianyu Zhan wrote:
> alloc_huge_page() now mixes normal code path with error handle logic.
> This patches move out the error handle logic, to make normal code
> path more clean and redue code duplicate.
> 
> Signed-off-by: Jianyu Zhan <nasa4836@gmail.com>

Acked-by: Davidlohr Bueso <davidlohr@hp.com>

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Re: [PATCH] mm, hugetlb: move the error handle logic out of normal code path

[Aneesh Kumar K.V]

Jianyu Zhan <nasa4836@gmail.com> writes:

> alloc_huge_page() now mixes normal code path with error handle logic.
> This patches move out the error handle logic, to make normal code
> path more clean and redue code duplicate.
>
> Signed-off-by: Jianyu Zhan <nasa4836@gmail.com>

Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

> ---
>  mm/hugetlb.c | 26 +++++++++++++-------------
>  1 file changed, 13 insertions(+), 13 deletions(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 26b1464..e81c69e 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1246,24 +1246,17 @@ static struct page *alloc_huge_page(struct vm_area_struct *vma,
>  			return ERR_PTR(-ENOSPC);
>  
>  	ret = hugetlb_cgroup_charge_cgroup(idx, pages_per_huge_page(h), &h_cg);
> -	if (ret) {
> -		if (chg || avoid_reserve)
> -			hugepage_subpool_put_pages(spool, 1);
> -		return ERR_PTR(-ENOSPC);
> -	}
> +	if (ret)
> +		goto out_subpool_put;
> +
>  	spin_lock(&hugetlb_lock);
>  	page = dequeue_huge_page_vma(h, vma, addr, avoid_reserve, chg);
>  	if (!page) {
>  		spin_unlock(&hugetlb_lock);
>  		page = alloc_buddy_huge_page(h, NUMA_NO_NODE);
> -		if (!page) {
> -			hugetlb_cgroup_uncharge_cgroup(idx,
> -						       pages_per_huge_page(h),
> -						       h_cg);
> -			if (chg || avoid_reserve)
> -				hugepage_subpool_put_pages(spool, 1);
> -			return ERR_PTR(-ENOSPC);
> -		}
> +		if (!page)
> +			goto out_uncharge_cgroup;
> +
>  		spin_lock(&hugetlb_lock);
>  		list_move(&page->lru, &h->hugepage_activelist);
>  		/* Fall through */
> @@ -1275,6 +1268,13 @@ static struct page *alloc_huge_page(struct vm_area_struct *vma,
>  
>  	vma_commit_reservation(h, vma, addr);
>  	return page;
> +
> +out_uncharge_cgroup:
> +	hugetlb_cgroup_uncharge_cgroup(idx, pages_per_huge_page(h), h_cg);
> +out_subpool_put:
> +	if (chg || avoid_reserve)
> +		hugepage_subpool_put_pages(spool, 1);
> +	return ERR_PTR(-ENOSPC);
>  }
>  
>  /*
> -- 
> 2.0.0-rc3
>
> --
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