Re: [PATCH v1 3/6] memcg-v1: no need for memcg locking for dirty tracking

Michal Hocko
2024-10-25T06:56:16Z

On Thu 24-10-24 18:23:00, Shakeel Butt wrote:
> During the era of memcg charge migration, the kernel has to be make sure
> that the dirty stat updates do not race with the charge migration.
> Otherwise it might update the dirty stats of the wrong memcg. Now with
> the memcg charge migration deprecated, there is no more race for dirty

s@deprecated@gone@

> stat updates and the previous locking can be removed.
>
> Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>

LGTM otherwise
Acked-by: Michal Hocko <mhocko@suse.com>

> ---
> fs/buffer.c | 5 -----
> mm/page-writeback.c | 16 +++-------------
> 2 files changed, 3 insertions(+), 18 deletions(-)
>
> diff --git a/fs/buffer.c b/fs/buffer.c
> index 1fc9a50def0b..88e765b0699f 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -736,15 +736,12 @@ bool block_dirty_folio(struct address_space *mapping, struct folio *folio)
> * Lock out page's memcg migration to keep PageDirty
> * synchronized with per-memcg dirty page counters.
> */
> - folio_memcg_lock(folio);
> newly_dirty = !folio_test_set_dirty(folio);
> spin_unlock(&mapping->i_private_lock);
>
> if (newly_dirty)
> __folio_mark_dirty(folio, mapping, 1);
>
> - folio_memcg_unlock(folio);
> -
> if (newly_dirty)
> __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
>
> @@ -1194,13 +1191,11 @@ void mark_buffer_dirty(struct buffer_head *bh)
> struct folio *folio = bh->b_folio;
> struct address_space *mapping = NULL;
>
> - folio_memcg_lock(folio);
> if (!folio_test_set_dirty(folio)) {
> mapping = folio->mapping;
> if (mapping)
> __folio_mark_dirty(folio, mapping, 0);
> }
> - folio_memcg_unlock(folio);
> if (mapping)
> __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
> }
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index 1d7179aba8e3..a76a73529fd9 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -2743,8 +2743,6 @@ EXPORT_SYMBOL(noop_dirty_folio);
> /*
> * Helper function for set_page_dirty family.
> *
> - * Caller must hold folio_memcg_lock().
> - *
> * NOTE: This relies on being atomic wrt interrupts.
> */
> static void folio_account_dirtied(struct folio *folio,
> @@ -2777,7 +2775,6 @@ static void folio_account_dirtied(struct folio *folio,
> /*
> * Helper function for deaccounting dirty page without writeback.
> *
> - * Caller must hold folio_memcg_lock().
> */
> void folio_account_cleaned(struct folio *folio, struct bdi_writeback *wb)
> {
> @@ -2795,9 +2792,8 @@ void folio_account_cleaned(struct folio *folio, struct bdi_writeback *wb)
> * If warn is true, then emit a warning if the folio is not uptodate and has
> * not been truncated.
> *
> - * The caller must hold folio_memcg_lock(). It is the caller's
> - * responsibility to prevent the folio from being truncated while
> - * this function is in progress, although it may have been truncated
> + * It is the caller's responsibility to prevent the folio from being truncated
> + * while this function is in progress, although it may have been truncated
> * before this function is called. Most callers have the folio locked.
> * A few have the folio blocked from truncation through other means (e.g.
> * zap_vma_pages() has it mapped and is holding the page table lock).
> @@ -2841,14 +2837,10 @@ void __folio_mark_dirty(struct folio *folio, struct address_space *mapping,
> */
> bool filemap_dirty_folio(struct address_space *mapping, struct folio *folio)
> {
> - folio_memcg_lock(folio);
> - if (folio_test_set_dirty(folio)) {
> - folio_memcg_unlock(folio);
> + if (folio_test_set_dirty(folio))
> return false;
> - }
>
> __folio_mark_dirty(folio, mapping, !folio_test_private(folio));
> - folio_memcg_unlock(folio);
>
> if (mapping->host) {
> /* !PageAnon && !swapper_space */
> @@ -2975,14 +2967,12 @@ void __folio_cancel_dirty(struct folio *folio)
> struct bdi_writeback *wb;
> struct wb_lock_cookie cookie = {};
>
> - folio_memcg_lock(folio);
> wb = unlocked_inode_to_wb_begin(inode, &cookie);
>
> if (folio_test_clear_dirty(folio))
> folio_account_cleaned(folio, wb);
>
> unlocked_inode_to_wb_end(inode, &cookie);
> - folio_memcg_unlock(folio);
> } else {
> folio_clear_dirty(folio);
> }
> --
> 2.43.5

--
Michal Hocko
SUSE Labs