mm/khugepaged: alloc_charge_hpage() take care of mem charge errors

PATCH Superseded Peter Xu 3 participants 5 messages Feb 21, 2023 – Feb 22, 2023

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Stable branch Memory management THP

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Peter Xu

author

2023-02-21 21:43 UTC #0 lore raw

PATCH 1/1 mm/khugepaged: alloc_charge_hpage() take care of mem charge errors

If memory charge failed, the caller shouldn't call mem_cgroup_uncharge(). Let alloc_charge_hpage() handle the error itself and clear hpage properly if mem charge fails.

Cc Johannes Weiner <[email protected]>

Cc Yang Shi <[email protected]>

Cc David Stevens <[email protected]>

Cc [email protected]

Fixes 9d82c69438d0 ("mm: memcontrol: convert anon and file-thp to new mem_cgroup_charge() API")

Signed-off-by Peter Xu <[email protected]>

---
 mm/khugepaged.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

mm/khugepaged.c +8 -1

index 8dbc39896811..941d1c7ea910 100644
@@ -1063,12 +1063,19 @@ static int alloc_charge_hpage(struct page **hpage, struct mm_struct *mm,
 	gfp_t gfp = (cc->is_khugepaged ? alloc_hugepage_khugepaged_gfpmask() :
 		     GFP_TRANSHUGE);
 	int node = hpage_collapse_find_target_node(cc);
+	struct folio *folio;
 
 	if (!hpage_collapse_alloc_page(hpage, gfp, node, &cc->alloc_nmask))
 		return SCAN_ALLOC_HUGE_PAGE_FAIL;
-	if (unlikely(mem_cgroup_charge(page_folio(*hpage), mm, gfp)))
+
+	folio = page_folio(*hpage);
+	if (unlikely(mem_cgroup_charge(folio, mm, gfp))) {
+		folio_put(folio);
+		*hpage = NULL;
 		return SCAN_CGROUP_CHARGE_FAIL;
+	}
 	count_memcg_page_event(*hpage, THP_COLLAPSE_ALLOC);
+
 	return SCAN_SUCCEED;
 }

Signature · 1 line

2.39.1

David Stevens

Reviewed-by on v1 1/1

2023-02-22 04:04 UTC #1 lore raw

Quoted 11 lines · Peter Xu

If memory charge failed, the caller shouldn't call mem_cgroup_uncharge(). Let alloc_charge_hpage() handle the error itself and clear hpage properly if mem charge fails.
Cc Johannes Weiner <[email protected]>
Cc Yang Shi <[email protected]>
Cc David Stevens <[email protected]>
Cc [email protected]
Fixes 9d82c69438d0 ("mm: memcontrol: convert anon and file-thp to new mem_cgroup_charge() API")
Signed-off-by Peter Xu <[email protected]>

Reviewed-by David Stevens <[email protected]>

Johannes Weiner

2023-02-22 17:06 UTC #2 lore raw

In reply to Peter Xu

Hello,

Quoted 3 lines · Peter Xu

If memory charge failed, the caller shouldn't call mem_cgroup_uncharge(). Let alloc_charge_hpage() handle the error itself and clear hpage properly if mem charge fails.

I'm a bit confused by this patch.

There isn't anything wrong with calling mem_cgroup_uncharge() on an uncharged page, functionally. It checks and bails out.

It's an unnecessary call of course, but since it's an error path it's also not a cost issue, either.

I could see an argument for improving the code, but this is actually more code, and the caller still has the uncharge-and-put branch anyway for when the collapse fails later on.

So I'm not sure I understand the benefit of this change.

Peter Xu

author

2023-02-22 17:38 UTC #3 lore raw

Quoted 11 lines · Johannes Weiner

Hello,
Quoted 3 lines · Peter Xu
If memory charge failed, the caller shouldn't call mem_cgroup_uncharge(). Let alloc_charge_hpage() handle the error itself and clear hpage properly if mem charge fails.
I'm a bit confused by this patch.
There isn't anything wrong with calling mem_cgroup_uncharge() on an uncharged page, functionally. It checks and bails out.

Indeed, I didn't really notice there's zero side effect of calling that, sorry. In that case both "Fixes" and "Cc: stable" do not apply.

Quoted 9 lines

It's an unnecessary call of course, but since it's an error path it's also not a cost issue, either.
I could see an argument for improving the code, but this is actually more code, and the caller still has the uncharge-and-put branch anyway for when the collapse fails later on.
So I'm not sure I understand the benefit of this change.

Yes, the benefit is having a clear interface for alloc_charge_hpage() with no prone to leaking huge page.

The patch comes from a review for David's other patch here:

https://lore.kernel.org/all/Y%2FU9fBxVJdhxiZ1v@x1n/

I've attached a new version just to reword and remove the inproper tags. Do you think that's acceptable?

Thanks,

Signature · 1 line

Peter Xu

From 0595acbd688b60ff7b2821a073c0fe857a4ae0ee Mon Sep 17 00:00:00 2001
From: Peter Xu <[email protected]>
Date: Tue, 21 Feb 2023 16:43:44 -0500
Subject: [PATCH] mm/khugepaged: alloc_charge_hpage() take care of mem charge
errors

If memory charge failed, instead of returning the hpage but with an error, allow the function to cleanup the folio properly, which is normally what a function should do in this case - either return successfully, or return with no side effect of partial runs with an indicated error.

This will also avoid the caller calling mem_cgroup_uncharge() unnecessarily with either anon or shmem path (even if it's safe to do so).

Cc Johannes Weiner <[email protected]>

Cc Yang Shi <[email protected]>

Cc David Stevens <[email protected]>

Signed-off-by Peter Xu <[email protected]>

---
 mm/khugepaged.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

mm/khugepaged.c +8 -1

index 8dbc39896811..941d1c7ea910 100644
@@ -1063,12 +1063,19 @@ static int alloc_charge_hpage(struct page **hpage, struct mm_struct *mm,
 	gfp_t gfp = (cc->is_khugepaged ? alloc_hugepage_khugepaged_gfpmask() :
 		     GFP_TRANSHUGE);
 	int node = hpage_collapse_find_target_node(cc);
+	struct folio *folio;
 
 	if (!hpage_collapse_alloc_page(hpage, gfp, node, &cc->alloc_nmask))
 		return SCAN_ALLOC_HUGE_PAGE_FAIL;
-	if (unlikely(mem_cgroup_charge(page_folio(*hpage), mm, gfp)))
+
+	folio = page_folio(*hpage);
+	if (unlikely(mem_cgroup_charge(folio, mm, gfp))) {
+		folio_put(folio);
+		*hpage = NULL;
 		return SCAN_CGROUP_CHARGE_FAIL;
+	}
 	count_memcg_page_event(*hpage, THP_COLLAPSE_ALLOC);
+
 	return SCAN_SUCCEED;
 }

Signature · 1 line

2.39.1

Johannes Weiner

Acked-by

2023-02-22 19:22 UTC #4 lore raw

Quoted 24 lines · Peter Xu

Quoted 11 lines · Johannes Weiner
Hello,
Quoted 3 lines · Peter Xu
If memory charge failed, the caller shouldn't call mem_cgroup_uncharge(). Let alloc_charge_hpage() handle the error itself and clear hpage properly if mem charge fails.
I'm a bit confused by this patch.
There isn't anything wrong with calling mem_cgroup_uncharge() on an uncharged page, functionally. It checks and bails out.
Indeed, I didn't really notice there's zero side effect of calling that, sorry. In that case both "Fixes" and "Cc: stable" do not apply.
Quoted 8 lines
It's an unnecessary call of course, but since it's an error path it's also not a cost issue, either.
I could see an argument for improving the code, but this is actually more code, and the caller still has the uncharge-and-put branch anyway for when the collapse fails later on.

Quoted 8 lines

Quoted 1 line
So I'm not sure I understand the benefit of this change.
Yes, the benefit is having a clear interface for alloc_charge_hpage() with no prone to leaking huge page.
The patch comes from a review for David's other patch here:
https://lore.kernel.org/all/Y%2FU9fBxVJdhxiZ1v@x1n/

Ah, that makes sense. Thanks for the context.

Quoted 11 lines

From 0595acbd688b60ff7b2821a073c0fe857a4ae0ee Mon Sep 17 00:00:00 2001
From: Peter Xu <[email protected]>
Date: Tue, 21 Feb 2023 16:43:44 -0500
Subject: [PATCH] mm/khugepaged: alloc_charge_hpage() take care of mem charge
errors
If memory charge failed, instead of returning the hpage but with an error, allow the function to cleanup the folio properly, which is normally what a function should do in this case - either return successfully, or return with no side effect of partial runs with an indicated error.

Quoted 7 lines

This will also avoid the caller calling mem_cgroup_uncharge() unnecessarily with either anon or shmem path (even if it's safe to do so).
Cc Johannes Weiner <[email protected]>
Cc Yang Shi <[email protected]>
Cc David Stevens <[email protected]>
Signed-off-by Peter Xu <[email protected]>

Acked-by Johannes Weiner <[email protected]>