[PATCH] mm: shmem: support large folio swap out fix 2

[Baolin Wang <baolin.wang@linux.alibaba.com>]

As Hugh said:
"
The i915 THP splitting inshmem_writepage() was to avoid mm VM_BUG_ONs and
crashes when shmem.c did not support huge page swapout: but now you are
enabling that support, and such VM_BUG_ONs and crashes are gone (so far
as I can see: and this is written on a laptop using the i915 driver).

I cannot think of why i915 itself would care how mm implements swapout
(beyond enjoying faster): I think all the wbc->split_large_folio you
introduce here should be reverted.
"

So this fixup patch will remove the wbc->split_large_folio as suggested
by Hugh.

Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
---
This fixup patch is based on 2024-08-28 mm-unstable branch.
Andrew, please help to squash this fixup patch. Thanks.
---
 drivers/gpu/drm/i915/gem/i915_gem_shmem.c | 1 -
 include/linux/writeback.h                 | 1 -
 mm/shmem.c                                | 9 ++++-----
 mm/vmscan.c                               | 4 +---
 4 files changed, 5 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_shmem.c b/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
index c66cb9c585e1..c5e1c718a6d2 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
@@ -308,7 +308,6 @@ void __shmem_writeback(size_t size, struct address_space *mapping)
 		.range_start = 0,
 		.range_end = LLONG_MAX,
 		.for_reclaim = 1,
-		.split_large_folio = 1,
 	};
 	unsigned long i;
 
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 10100e22d5c6..51278327b3c6 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -63,7 +63,6 @@ struct writeback_control {
 	unsigned range_cyclic:1;	/* range_start is cyclic */
 	unsigned for_sync:1;		/* sync(2) WB_SYNC_ALL writeback */
 	unsigned unpinned_netfs_wb:1;	/* Cleared I_PINNING_NETFS_WB */
-	unsigned split_large_folio:1;	/* Split large folio for shmem writeback */
 
 	/*
 	 * When writeback IOs are bounced through async layers, only the
diff --git a/mm/shmem.c b/mm/shmem.c
index 16099340ca1d..2b0209d6ac9c 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1473,19 +1473,18 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc)
 		goto redirty;
 
 	/*
-	 * If /sys/kernel/mm/transparent_hugepage/shmem_enabled is "always" or
-	 * "force", drivers/gpu/drm/i915/gem/i915_gem_shmem.c gets huge pages,
-	 * and its shmem_writeback() needs them to be split when swapping.
+	 * If CONFIG_THP_SWAP is not enabled, the large folio should be
+	 * split when swapping.
 	 *
 	 * And shrinkage of pages beyond i_size does not split swap, so
 	 * swapout of a large folio crossing i_size needs to split too
 	 * (unless fallocate has been used to preallocate beyond EOF).
 	 */
 	if (folio_test_large(folio)) {
-		split = wbc->split_large_folio;
 		index = shmem_fallocend(inode,
 			DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE));
-		if (index > folio->index && index < folio_next_index(folio))
+		if ((index > folio->index && index < folio_next_index(folio)) ||
+		    !IS_ENABLED(CONFIG_THP_SWAP))
 			split = true;
 	}
 
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 283e3f9d652b..f27792e77a0f 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -681,10 +681,8 @@ static pageout_t pageout(struct folio *folio, struct address_space *mapping,
 		 * not enabled or contiguous swap entries are failed to
 		 * allocate.
 		 */
-		if (shmem_mapping(mapping) && folio_test_large(folio)) {
+		if (shmem_mapping(mapping) && folio_test_large(folio))
 			wbc.list = folio_list;
-			wbc.split_large_folio = !IS_ENABLED(CONFIG_THP_SWAP);
-		}
 
 		folio_set_reclaim(folio);
 		res = mapping->a_ops->writepage(&folio->page, &wbc);
-- 
2.39.3