linux-kernel - [PATCH 4/7] mm: shmem: handle special case of shmem_recalc

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Message-Id: <20250605221037.7872-5-shikemeng@huaweicloud.com>
Date: Fri,  6 Jun 2025 06:10:34 +0800
From: Kemeng Shi <shikemeng@...weicloud.com>
To: hughd@...gle.com,
	baolin.wang@...ux.alibaba.com,
	willy@...radead.org,
	akpm@...ux-foundation.org
Cc: linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: [PATCH 4/7] mm: shmem: handle special case of shmem_recalc_inode() in it's caller

The sepcial case in shmem_recalc_inode() is tailored for shmem_writepage().
By raising swapped before nrpages is lowered directly within
shmem_writepage(), we can simplify code of shmem_recalc_inode() and
eliminate the need of executing the special case code for all callers of
shmem_recalc_inode().

Signed-off-by: Kemeng Shi <shikemeng@...weicloud.com>
---
 mm/shmem.c | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index 2349673b239b..9f5e1eccaacb 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -443,15 +443,6 @@ static void shmem_recalc_inode(struct inode *inode, long alloced, long swapped)
 	info->swapped += swapped;
 	freed = info->alloced - info->swapped -
 		READ_ONCE(inode->i_mapping->nrpages);
-	/*
-	 * Special case: whereas normally shmem_recalc_inode() is called
-	 * after i_mapping->nrpages has already been adjusted (up or down),
-	 * shmem_writepage() has to raise swapped before nrpages is lowered -
-	 * to stop a racing shmem_recalc_inode() from thinking that a page has
-	 * been freed.  Compensate here, to avoid the need for a followup call.
-	 */
-	if (swapped > 0)
-		freed += swapped;
 	if (freed > 0)
 		info->alloced -= freed;
 	spin_unlock(&info->lock);
@@ -1694,9 +1685,16 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc)
 		list_add(&info->swaplist, &shmem_swaplist);
 
 	if (!folio_alloc_swap(folio, __GFP_HIGH | __GFP_NOMEMALLOC | __GFP_NOWARN)) {
-		shmem_recalc_inode(inode, 0, nr_pages);
+		/*
+		 * Raise swapped before nrpages is lowered to stop racing
+		 * shmem_recalc_inode() from thinking that a page has been freed.
+		 */
+		spin_lock(&info->lock);
+		info->swapped += nr_pages;
+		spin_unlock(&info->lock);
 		swap_shmem_alloc(folio->swap, nr_pages);
 		shmem_delete_from_page_cache(folio, swp_to_radix_entry(folio->swap));
+		shmem_recalc_inode(inode, 0, 0);
 
 		mutex_unlock(&shmem_swaplist_mutex);
 		BUG_ON(folio_mapped(folio));
-- 
2.30.0