memcg-v1: no need for memcg locking for writeback tracking

During the era of memcg charge migration, the kernel has to be make
sure that the writeback stat updates do not race with the charge
migration.  Otherwise it might update the writeback stats of the wrong
memcg.  Now with the memcg charge migration gone, there is no more race
for writeback stat updates and the previous locking can be removed.

Link: https://lkml.kernel.org/r/20241025012304.2473312-5-shakeel.butt@linux.dev
Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Roman Gushchin <roman.gushchin@linux.dev>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index a76a73529fd9cd06f8e1a67c5bb540044b753fc8..9c3317c3a6155fee4105ebc8bac2d51747e3bf73 100644 (file)
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -3083,7 +3083,6 @@ bool __folio_end_writeback(struct folio *folio)
        struct address_space *mapping = folio_mapping(folio);
        bool ret;
 
-       folio_memcg_lock(folio);
        if (mapping && mapping_use_writeback_tags(mapping)) {
                struct inode *inode = mapping->host;
                struct backing_dev_info *bdi = inode_to_bdi(inode);
@@ -3114,7 +3113,6 @@ bool __folio_end_writeback(struct folio *folio)
        lruvec_stat_mod_folio(folio, NR_WRITEBACK, -nr);
        zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, -nr);
        node_stat_mod_folio(folio, NR_WRITTEN, nr);
-       folio_memcg_unlock(folio);
 
        return ret;
 }
@@ -3127,7 +3125,6 @@ void __folio_start_writeback(struct folio *folio, bool keep_write)
 
        VM_BUG_ON_FOLIO(folio_test_writeback(folio), folio);
 
-       folio_memcg_lock(folio);
        if (mapping && mapping_use_writeback_tags(mapping)) {
                XA_STATE(xas, &mapping->i_pages, folio_index(folio));
                struct inode *inode = mapping->host;
@@ -3168,7 +3165,6 @@ void __folio_start_writeback(struct folio *folio, bool keep_write)
 
        lruvec_stat_mod_folio(folio, NR_WRITEBACK, nr);
        zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, nr);
-       folio_memcg_unlock(folio);
 
        access_ret = arch_make_folio_accessible(folio);
        /*