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

[Minchan Kim]

On Mon, Apr 27, 2026 at 11:29:14AM +0200, David Hildenbrand (Arm) wrote:
> On 4/24/26 23:24, Minchan Kim wrote:
> > On Fri, Apr 24, 2026 at 09:56:01AM +0200, David Hildenbrand (Arm) wrote:
> >> On 4/22/26 01:02, Minchan Kim wrote:
> >>
> >> Can we make the subject easier to understand?
> >>
> >> "mm: process_mrelease: evict clean file folios when reaping a process"
> >>
> >>> 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@xxxxxxxxxx>
> >>> ---
> >>>  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.
> >>
> >> There is no such parameter.
> >>
> >> But I do wonder if such a parameter would be better than passing in the MM here.
> > 
> > Makes sense.
> > 
> >>
> >> Also, is there a way to avoid moving the function?
> > 
> > I guess you are talking about "free_pages_and_swap_cache".
> > 
> > The problem is mm/swap_state.c is conditionally compiled only when CONFIG_SWAP
> > is enabled.
> > 
> > Since the expedited clean file cache eviction should be available
> > even on !CONFIG_SWAP, we need this function to be compiled unconditionally.
> > That is why I moved it to swap.c, which is always compiled.
> 
> Ah, right. Please spell that out in the patch description!

Acked.