Re: [PATCH v1 1/3] mm: process_mrelease: expedite clean file folio reclaim via mmu_gather

[Alexander Gordeev <agordeev@linux.ibm.com>]

On Tue, Apr 21, 2026 at 04:02:37PM -0700, Minchan Kim wrote:

Hi Minchan,

> Currently, process_mrelease() unmaps pages but file-backed pages are
> not evicted and stay in the pagecache, relying on standard memory reclaim
> (kswapd or direct reclaim) to eventually free them. This delays the
> immediate recovery of system memory under Android's LMKD scenarios,
> leading to redundant background apps kills.
> 
> This patch implements an expedited eviction mechanism for clean pagecache
> folios in the mmu_gather code, similar to how swapcache folios are handled.
> It drops them from the pagecache (i.e., evicting them) if they are completely
> unmapped during reaping.
> 
> Within this single unified loop, anonymous pages are released via
> free_swap_cache(), and file-backed folios are symmetrically released via
> free_file_cache().
> 
> Signed-off-by: Minchan Kim <minchan@kernel.org>
> ---
>  arch/s390/include/asm/tlb.h |  2 +-
>  include/linux/swap.h        |  5 ++---
>  mm/mmu_gather.c             |  7 ++++---
>  mm/swap.c                   | 42 +++++++++++++++++++++++++++++++++++++
>  mm/swap_state.c             | 26 -----------------------
>  5 files changed, 49 insertions(+), 33 deletions(-)
> 
> diff --git a/arch/s390/include/asm/tlb.h b/arch/s390/include/asm/tlb.h
> index 619fd41e710e..2736dbb571a8 100644
> --- a/arch/s390/include/asm/tlb.h
> +++ b/arch/s390/include/asm/tlb.h
> @@ -62,7 +62,7 @@ static inline bool __tlb_remove_folio_pages(struct mmu_gather *tlb,
>  	VM_WARN_ON_ONCE(delay_rmap);
>  	VM_WARN_ON_ONCE(page_folio(page) != page_folio(page + nr_pages - 1));
>  
> -	free_pages_and_swap_cache(encoded_pages, ARRAY_SIZE(encoded_pages));
> +	free_pages_and_caches(tlb->mm, encoded_pages, ARRAY_SIZE(encoded_pages));
>  	return false;
>  }
>  
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index 62fc7499b408..bdb784966343 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -414,7 +414,9 @@ extern int sysctl_min_unmapped_ratio;
>  extern int sysctl_min_slab_ratio;
>  #endif
>  
> +struct mm_struct;
>  void check_move_unevictable_folios(struct folio_batch *fbatch);
> +void free_pages_and_caches(struct mm_struct *mm, struct encoded_page **pages, int nr);
>  
>  extern void __meminit kswapd_run(int nid);
>  extern void __meminit kswapd_stop(int nid);
> @@ -433,7 +435,6 @@ static inline unsigned long total_swapcache_pages(void)
>  
>  void free_swap_cache(struct folio *folio);
>  void free_folio_and_swap_cache(struct folio *folio);
> -void free_pages_and_swap_cache(struct encoded_page **, int);
>  /* linux/mm/swapfile.c */
>  extern atomic_long_t nr_swap_pages;
>  extern long total_swap_pages;
> @@ -510,8 +511,6 @@ static inline void put_swap_device(struct swap_info_struct *si)
>  	do { (val)->freeswap = (val)->totalswap = 0; } while (0)
>  #define free_folio_and_swap_cache(folio) \
>  	folio_put(folio)
> -#define free_pages_and_swap_cache(pages, nr) \
> -	release_pages((pages), (nr));
>  
>  static inline void free_swap_cache(struct folio *folio)
>  {
> diff --git a/mm/mmu_gather.c b/mm/mmu_gather.c
> index fe5b6a031717..3c6c315d3c48 100644
> --- a/mm/mmu_gather.c
> +++ b/mm/mmu_gather.c
> @@ -100,7 +100,8 @@ void tlb_flush_rmaps(struct mmu_gather *tlb, struct vm_area_struct *vma)
>   */
>  #define MAX_NR_FOLIOS_PER_FREE		512
>  
> -static void __tlb_batch_free_encoded_pages(struct mmu_gather_batch *batch)
> +static void __tlb_batch_free_encoded_pages(struct mm_struct *mm,
> +		struct mmu_gather_batch *batch)
>  {
>  	struct encoded_page **pages = batch->encoded_pages;
>  	unsigned int nr, nr_pages;
> @@ -135,7 +136,7 @@ static void __tlb_batch_free_encoded_pages(struct mmu_gather_batch *batch)
>  			}
>  		}
>  
> -		free_pages_and_swap_cache(pages, nr);
> +		free_pages_and_caches(mm, pages, nr);
>  		pages += nr;
>  		batch->nr -= nr;
>  
> @@ -148,7 +149,7 @@ static void tlb_batch_pages_flush(struct mmu_gather *tlb)
>  	struct mmu_gather_batch *batch;
>  
>  	for (batch = &tlb->local; batch && batch->nr; batch = batch->next)
> -		__tlb_batch_free_encoded_pages(batch);
> +		__tlb_batch_free_encoded_pages(tlb->mm, batch);
>  	tlb->active = &tlb->local;
>  }
>  
> diff --git a/mm/swap.c b/mm/swap.c
> index bb19ccbece46..e44bc8cefceb 100644
> --- a/mm/swap.c
> +++ b/mm/swap.c
> @@ -1043,6 +1043,48 @@ void release_pages(release_pages_arg arg, int nr)
>  }
>  EXPORT_SYMBOL(release_pages);
>  
> +static inline void free_file_cache(struct folio *folio)
> +{
> +	if (folio_trylock(folio)) {
> +		mapping_evict_folio(folio_mapping(folio), folio);
> +		folio_unlock(folio);
> +	}
> +}
> +
> +/*
> + * Passed an array of pages, drop them all from swapcache and then release
> + * them.  They are removed from the LRU and freed if this is their last use.
> + *
> + * If @try_evict_file_folios is true, this function will proactively evict clean
> + * file-backed folios if they are no longer mapped.
> + */
> +void free_pages_and_caches(struct mm_struct *mm, struct encoded_page **pages, int nr)
> +{
> +	bool try_evict_file_folios = mm_flags_test(MMF_UNSTABLE, mm);
> +	struct folio_batch folios;
> +	unsigned int refs[PAGEVEC_SIZE];
> +
> +	folio_batch_init(&folios);
> +	for (int i = 0; i < nr; i++) {
> +		struct folio *folio = page_folio(encoded_page_ptr(pages[i]));
> +
> +		if (folio_test_anon(folio))
> +			free_swap_cache(folio);
> +		else if (unlikely(try_evict_file_folios))
> +			free_file_cache(folio);

This condition is absent in free_pages_and_swap_cache().
What would happen with non-anon and non-evict folio?

> +
> +		refs[folios.nr] = 1;
> +		if (unlikely(encoded_page_flags(pages[i]) &
> +			     ENCODED_PAGE_BIT_NR_PAGES_NEXT))
> +			refs[folios.nr] = encoded_nr_pages(pages[++i]);
> +
> +		if (folio_batch_add(&folios, folio) == 0)
> +			folios_put_refs(&folios, refs);
> +	}
> +	if (folios.nr)
> +		folios_put_refs(&folios, refs);
> +}
> +
>  /*
>   * The folios which we're about to release may be in the deferred lru-addition
>   * queues.  That would prevent them from really being freed right now.  That's
> diff --git a/mm/swap_state.c b/mm/swap_state.c
> index 6d0eef7470be..7576bf36d920 100644
> --- a/mm/swap_state.c
> +++ b/mm/swap_state.c
> @@ -400,32 +400,6 @@ void free_folio_and_swap_cache(struct folio *folio)
>  		folio_put(folio);
>  }
>  
> -/*
> - * Passed an array of pages, drop them all from swapcache and then release
> - * them.  They are removed from the LRU and freed if this is their last use.
> - */
> -void free_pages_and_swap_cache(struct encoded_page **pages, int nr)
> -{
> -	struct folio_batch folios;
> -	unsigned int refs[PAGEVEC_SIZE];
> -
> -	folio_batch_init(&folios);
> -	for (int i = 0; i < nr; i++) {
> -		struct folio *folio = page_folio(encoded_page_ptr(pages[i]));
> -
> -		free_swap_cache(folio);
> -		refs[folios.nr] = 1;
> -		if (unlikely(encoded_page_flags(pages[i]) &
> -			     ENCODED_PAGE_BIT_NR_PAGES_NEXT))
> -			refs[folios.nr] = encoded_nr_pages(pages[++i]);
> -
> -		if (folio_batch_add(&folios, folio) == 0)
> -			folios_put_refs(&folios, refs);
> -	}
> -	if (folios.nr)
> -		folios_put_refs(&folios, refs);
> -}
> -
>  static inline bool swap_use_vma_readahead(void)
>  {
>  	return READ_ONCE(enable_vma_readahead) && !atomic_read(&nr_rotate_swap);
> -- 
> 2.54.0.rc1.555.g9c883467ad-goog
> 
>