Re: [PATCH v5] mm: shrink skip folio mapped by an exiting process

[David Hildenbrand <david@redhat.com>]

On 08.07.24 11:04, Zhiguo Jiang wrote:
> The releasing process of the non-shared anonymous folio mapped solely by
> an exiting process may go through two flows: 1) the anonymous folio is
> firstly is swaped-out into swapspace and transformed into a swp_entry
> in shrink_folio_list; 2) then the swp_entry is released in the process
> exiting flow. This will increase the cpu load of releasing a non-shared
> anonymous folio mapped solely by an exiting process, because the folio
> go through swap-out and the releasing the swapspace and swp_entry.
> 
> When system is low memory, it is more likely to occur, because more
> backend applidatuions will be killed.
> 
> The modification is that shrink skips the non-shared anonymous folio
> solely mapped by an exting process and the folio is only released
> directly in the process exiting flow, which will save swap-out time
> and alleviate the load of the process exiting.
> 
> Signed-off-by: Zhiguo Jiang <justinjiang@vivo.com>
> ---
> 
> Change log:
> v4->v5:
> 1.Modify to skip non-shared anonymous folio only.
> 2.Update comments for pra->referenced = -1.
> v3->v4:
> 1.Modify that the unshared folios mapped only in exiting task are skip.
> v2->v3:
> Nothing.
> v1->v2:
> 1.The VM_EXITING added in v1 patch is removed, because it will fail
> to compile in 32-bit system.
> 
>   mm/rmap.c   | 13 +++++++++++++
>   mm/vmscan.c |  7 ++++++-
>   2 files changed, 19 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 26806b49a86f..5b5281d71dbb
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -843,6 +843,19 @@ static bool folio_referenced_one(struct folio *folio,
>   	int referenced = 0;
>   	unsigned long start = address, ptes = 0;
>   
> +	/*
> +	 * Skip the non-shared anonymous folio mapped solely by
> +	 * the single exiting process, and release it directly
> +	 * in the process exiting.
> +	 */
> +	if ((!atomic_read(&vma->vm_mm->mm_users) ||
> +		test_bit(MMF_OOM_SKIP, &vma->vm_mm->flags)) &&
> +		folio_test_anon(folio) && folio_test_swapbacked(folio) &&
> +		!folio_likely_mapped_shared(folio)) {

I'm currently working on moving all folio_likely_mapped_shared() under 
the PTL, where we are then sure that the folio is actually mapped by 
this process (e.g., no concurrent unmapping poisslbe).

Can we do the same here directly?

-- 
Cheers,

David / dhildenb