linux-kernel - [RFC 26/43] mm: shmem: when inserting, handle pages already charged to a memcg

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Date:   Wed,  6 May 2020 17:41:52 -0700
From:   Anthony Yznaga <anthony.yznaga@...cle.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:     willy@...radead.org, corbet@....net, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, x86@...nel.org, hpa@...or.com,
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Subject: [RFC 26/43] mm: shmem: when inserting, handle pages already charged to a memcg

If shmem_insert_page() is called to insert a page that was preserved
using PKRAM on the current boot (i.e. preserved page is restored without
an intervening kexec boot), the page will still be charged to a memory
cgroup because it is never freed. Don't try to charge it again.

Signed-off-by: Anthony Yznaga <anthony.yznaga@...cle.com>
---
 mm/shmem.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index 13475073fb52..1f3b43b8fa34 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -693,6 +693,7 @@ int shmem_insert_page(struct mm_struct *mm, struct inode *inode, pgoff_t index,
 	struct mem_cgroup *memcg;
 	pgoff_t hindex = index;
 	bool on_lru = PageLRU(page);
+	bool has_memcg = page->mem_cgroup ? true : false;
 
 	if (index > (MAX_LFS_FILESIZE >> PAGE_SHIFT))
 		return -EFBIG;
@@ -738,20 +739,24 @@ int shmem_insert_page(struct mm_struct *mm, struct inode *inode, pgoff_t index,
 
 	__SetPageReferenced(page);
 
-	err = mem_cgroup_try_charge_delay(page, mm, gfp, &memcg,
-					PageTransHuge(page));
-	if (err)
-		goto out_unlock;
+	if (!has_memcg) {
+		err = mem_cgroup_try_charge_delay(page, mm, gfp, &memcg,
+						PageTransHuge(page));
+		if (err)
+			goto out_unlock;
+	}
 
 	err = shmem_add_to_page_cache(page, mapping, hindex,
 					NULL, gfp & GFP_RECLAIM_MASK);
 	if (err) {
-		mem_cgroup_cancel_charge(page, memcg,
-			PageTransHuge(page));
+		if (!has_memcg)
+			mem_cgroup_cancel_charge(page, memcg,
+						PageTransHuge(page));
 		goto out_unlock;
 	}
-	mem_cgroup_commit_charge(page, memcg, on_lru,
-			PageTransHuge(page));
+	if (!has_memcg)
+		mem_cgroup_commit_charge(page, memcg, on_lru,
+					PageTransHuge(page));
 
 	if (!on_lru)
 		lru_cache_add_anon(page);
-- 
2.13.3