Commit 3c06ee7c authored by Lorenzo Stoakes's avatar Lorenzo Stoakes Committed by Andrew Morton
Browse files

mm/vma: remove mmap() retry merge 

We have now introduced a mechanism that obviates the need for a
reattempted merge via the mmap_prepare() file hook, so eliminate this
functionality altogether.

The retry merge logic has been the cause of a great deal of complexity in
the past and required a great deal of careful manoeuvring of code to
ensure its continued and correct functionality.

It has also recently been involved in an issue surrounding maple tree
state, which again points to its problematic nature.

We make it much easier to reason about mmap() logic by eliminating this
and simply writing a VMA once.  This also opens the doors to future
optimisation and improvement in the mmap() logic.

For any device or file system which encounters unwanted VMA fragmentation
as a result of this change (that is, having not implemented .mmap_prepare
hooks), the issue is easily resolvable by doing so.

Link: https://lkml.kernel.org/r/d5d8fc74f02b89d6bec5ae8bc0e36d7853b65cda.1746792520.git.lorenzo.stoakes@oracle.com


Signed-off-by: default avatarLorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: default avatarDavid Hildenbrand <david@redhat.com>
Reviewed-by: default avatarVlastimil Babka <vbabka@suse.cz>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 439b3fb0

mm/vma.c

+0 −14
Original line number Diff line number Diff line
@@ -24,7 +24,6 @@ struct mmap_state { 
	void *vm_private_data;



	unsigned long charged;

	bool retry_merge;



	struct vm_area_struct *prev;

	struct vm_area_struct *next;
@@ -2417,8 +2416,6 @@ static int __mmap_new_file_vma(struct mmap_state *map, 
			!(map->flags & VM_MAYWRITE) &&

			(vma->vm_flags & VM_MAYWRITE));



	/* If the flags change (and are mergeable), let's retry later. */

	map->retry_merge = vma->vm_flags != map->flags && !(vma->vm_flags & VM_SPECIAL);

	map->flags = vma->vm_flags;



	return 0;
@@ -2622,17 +2619,6 @@ static unsigned long __mmap_region(struct file *file, unsigned long addr, 
	if (have_mmap_prepare)

		set_vma_user_defined_fields(vma, &map);



	/* If flags changed, we might be able to merge, so try again. */

	if (map.retry_merge) {

		struct vm_area_struct *merged;

		VMG_MMAP_STATE(vmg, &map, vma);



		vma_iter_config(map.vmi, map.addr, map.end);

		merged = vma_merge_existing_range(&vmg);

		if (merged)

			vma = merged;

	}



	__mmap_complete(&map, vma);



	return addr;