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

David Hildenbrand (Arm)
2026-04-24T07:56:07Z

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@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.

There is no such parameter.

But I do wonder if such a parameter would be better than passing in the MM here.

Also, is there a way to avoid moving the function?

--
Cheers,

David