Commit 7716506a authored by Matthew Wilcox (Oracle)'s avatar Matthew Wilcox (Oracle) Committed by Linus Torvalds
Browse files

mm: introduce and use mapping_empty() 

Patch series "Remove nrexceptional tracking", v2.

We actually use nrexceptional for very little these days.  It's a minor
pain to keep in sync with nrpages, but the pain becomes much bigger with
the THP patches because we don't know how many indices a shadow entry
occupies.  It's easier to just remove it than keep it accurate.

Also, we save 8 bytes per inode which is nothing to sneeze at; on my
laptop, it would improve shmem_inode_cache from 22 to 23 objects per
16kB, and inode_cache from 26 to 27 objects.  Combined, that saves
a megabyte of memory from a combined usage of 25MB for both caches.
Unfortunately, ext4 doesn't cross a magic boundary, so it doesn't save
any memory for ext4.

This patch (of 4):

Instead of checking the two counters (nrpages and nrexceptional), we can
just check whether i_pages is empty.

Link: https://lkml.kernel.org/r/20201026151849.24232-1-willy@infradead.org
Link: https://lkml.kernel.org/r/20201026151849.24232-2-willy@infradead.org


Signed-off-by: default avatarMatthew Wilcox (Oracle) <willy@infradead.org>
Tested-by: default avatarVishal Verma <vishal.l.verma@intel.com>
Acked-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 4d75136b

fs/block_dev.c

+1 −1
Original line number Diff line number Diff line
@@ -79,7 +79,7 @@ static void kill_bdev(struct block_device *bdev) 
{

	struct address_space *mapping = bdev->bd_inode->i_mapping;



	if (mapping->nrpages == 0 && mapping->nrexceptional == 0)

	if (mapping_empty(mapping))

		return;



	invalidate_bh_lrus();

fs/dax.c

+1 −1
Original line number Diff line number Diff line
@@ -965,7 +965,7 @@ int dax_writeback_mapping_range(struct address_space *mapping, 
	if (WARN_ON_ONCE(inode->i_blkbits != PAGE_SHIFT))

		return -EIO;



	if (!mapping->nrexceptional || wbc->sync_mode != WB_SYNC_ALL)

	if (mapping_empty(mapping) || wbc->sync_mode != WB_SYNC_ALL)

		return 0;



	trace_dax_writeback_range(inode, xas.xa_index, end_index);

fs/gfs2/glock.c

+1 −2
Original line number Diff line number Diff line
@@ -273,8 +273,7 @@ static void __gfs2_glock_put(struct gfs2_glock *gl) 
	if (mapping) {

		truncate_inode_pages_final(mapping);

		if (!gfs2_withdrawn(sdp))

			GLOCK_BUG_ON(gl, mapping->nrpages ||

				     mapping->nrexceptional);

			GLOCK_BUG_ON(gl, !mapping_empty(mapping));

	}

	trace_gfs2_glock_put(gl);

	sdp->sd_lockstruct.ls_ops->lm_put_lock(gl);

include/linux/pagemap.h

+5 −0
Original line number Diff line number Diff line
@@ -18,6 +18,11 @@ 


struct pagevec;



static inline bool mapping_empty(struct address_space *mapping)

{

	return xa_empty(&mapping->i_pages);

}



/*

 * Bits in mapping->flags.

 */

mm/truncate.c

+3 −15
Original line number Diff line number Diff line
@@ -295,7 +295,7 @@ void truncate_inode_pages_range(struct address_space *mapping, 
	pgoff_t		index;

	int		i;



	if (mapping->nrpages == 0 && mapping->nrexceptional == 0)

	if (mapping_empty(mapping))

		goto out;



	/* Offsets within partial pages */
@@ -440,9 +440,6 @@ EXPORT_SYMBOL(truncate_inode_pages); 
 */

void truncate_inode_pages_final(struct address_space *mapping)

{

	unsigned long nrexceptional;

	unsigned long nrpages;



	/*

	 * Page reclaim can not participate in regular inode lifetime

	 * management (can't call iput()) and thus can race with the
@@ -452,16 +449,7 @@ void truncate_inode_pages_final(struct address_space *mapping) 
	 */

	mapping_set_exiting(mapping);



	/*

	 * When reclaim installs eviction entries, it increases

	 * nrexceptional first, then decreases nrpages.  Make sure we see

	 * this in the right order or we might miss an entry.

	 */

	nrpages = mapping->nrpages;

	smp_rmb();

	nrexceptional = mapping->nrexceptional;



	if (nrpages || nrexceptional) {

	if (!mapping_empty(mapping)) {

		/*

		 * As truncation uses a lockless tree lookup, cycle

		 * the tree lock to make sure any ongoing tree
@@ -633,7 +621,7 @@ int invalidate_inode_pages2_range(struct address_space *mapping, 
	int ret2 = 0;

	int did_range_unmap = 0;



	if (mapping->nrpages == 0 && mapping->nrexceptional == 0)

	if (mapping_empty(mapping))

		goto out;



	pagevec_init(&pvec);