[PATCH mm-hotfixses] Revert "mm: limit filemap_fault readahead to VMA boundaries"

[Lorenzo Stoakes <ljs@kernel.org>]

This reverts commit 7b32f64bc512b40b268776c5ac4d354b325b3197.

This patch caused a significant performance regression, so revert it, and
we can determine whether the approach is sensible or not moving forwards,
and if so how to avoid this.

There was a merge conflict with commit de97ae6222c1 ("mm/readahead: no
PG_readahead on EOF"), care was taken to ensure that the revert retained the
behaviour of this patch and cleanly reverts commit 7b32f64bc512 ("mm: limit
filemap_fault readahead to VMA boundaries") only.

Fixes: 7b32f64bc512 ("mm: limit filemap_fault readahead to VMA boundaries")
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202606181547.617a6967-lkp@intel.com
Signed-off-by: Lorenzo Stoakes <ljs@kernel.org>
---
 include/linux/pagemap.h | 2 --
 mm/filemap.c            | 4 ----
 mm/readahead.c          | 6 +-----
 3 files changed, 1 insertion(+), 11 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 627771e82eb1..2c3718d592d6 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -1348,7 +1348,6 @@ struct readahead_control {
 	struct file_ra_state *ra;
 /* private: use the readahead_* accessors instead */
 	pgoff_t _index;
-	pgoff_t _max_index; /* limit readahead to _max_index, inclusive */
 	unsigned int _nr_pages;
 	unsigned int _batch_count;
 	bool dropbehind;
@@ -1362,7 +1361,6 @@ struct readahead_control {
 		.mapping = m,						\
 		.ra = r,						\
 		._index = i,						\
-		._max_index = ULONG_MAX,				\
 	}

 #define VM_READAHEAD_PAGES	(SZ_128K / PAGE_SIZE)
diff --git a/mm/filemap.c b/mm/filemap.c
index dc3a0e960b9f..17a64837597c 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -3312,8 +3312,6 @@ static struct file *do_sync_mmap_readahead(struct vm_fault *vmf)
 	unsigned int thp_order = 0;
 	unsigned short mmap_miss;

-	ractl._max_index = vmf->vma->vm_pgoff + vma_pages(vmf->vma) - 1;
-
 	/* Use the readahead code, even if readahead is disabled */
 	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && (vm_flags & VM_HUGEPAGE)) {
 		/*
@@ -3409,7 +3407,6 @@ static struct file *do_sync_mmap_readahead(struct vm_fault *vmf)
 		 * mmap read-around
 		 */
 		ra->start = max_t(long, 0, vmf->pgoff - ra->ra_pages / 2);
-		ra->start = max(ra->start, vmf->vma->vm_pgoff);
 		ra->size = ra->ra_pages;
 		ra->async_size = ra->ra_pages / 4;
 		ra->order = 0;
@@ -3457,7 +3454,6 @@ static struct file *do_async_mmap_readahead(struct vm_fault *vmf,
 	}

 	if (folio_test_readahead(folio)) {
-		ractl._max_index = vmf->vma->vm_pgoff + vma_pages(vmf->vma) - 1;
 		fpin = maybe_unlock_mmap_for_io(vmf, fpin);
 		page_cache_async_ra(&ractl, folio, ra->ra_pages);
 	}
diff --git a/mm/readahead.c b/mm/readahead.c
index 38ce16e3fcbd..558c92957518 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -335,8 +335,6 @@ static void do_page_cache_ra(struct readahead_control *ractl,
 		return;

 	end_index = (isize - 1) >> PAGE_SHIFT;
-	if (end_index > ractl->_max_index)
-		end_index = ractl->_max_index;
 	if (index > end_index)
 		return;
 	/* Don't read past the page containing the last byte of the file */
@@ -487,7 +485,7 @@ void page_cache_ra_order(struct readahead_control *ractl,
 	pgoff_t start = readahead_index(ractl);
 	pgoff_t index = start;
 	unsigned int min_order = mapping_min_folio_order(mapping);
-	pgoff_t limit;
+	pgoff_t limit = (i_size_read(mapping->host) - 1) >> PAGE_SHIFT;
 	pgoff_t mark;
 	unsigned int nofs;
 	int err = 0;
@@ -500,8 +498,6 @@ void page_cache_ra_order(struct readahead_control *ractl,
 		goto fallback;
 	}

-	limit = (i_size_read(mapping->host) - 1) >> PAGE_SHIFT;
-	limit = min(limit, ractl->_max_index);
 	if (limit > index + ra->size - 1) {
 		limit = index + ra->size - 1;
 		mark = index + ra->size - ra->async_size;
--
2.54.0