Re: linux-next: manual merge of the random tree with the mm-stable tree

[Stephen Rothwell <sfr@canb.auug.org.au>]

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Hi all,

On Tue, 9 Jul 2024 17:40:53 +1000 Stephen Rothwell <sfr@canb.auug.org.au> wrote:
> 
> Today's linux-next merge of the random tree got a conflict in:
> 
>   mm/rmap.c
> 
> between commits:
> 
>   26d21b18d971 ("mm/rmap: remove duplicated exit code in pagewalk loop")
>   15bde4abab73 ("mm: extend rmap flags arguments for folio_add_new_anon_rmap")
> 
> from the mm-stable tree and commit:
> 
>   94beef29e110 ("mm: add MAP_DROPPABLE for designating always lazily freeable mappings")
> 
> from the random tree.
> 
> I fixed it up (see below) and can carry the fix as necessary. This
> is now fixed as far as linux-next is concerned, but any non trivial
> conflicts should be mentioned to your upstream maintainer when your tree
> is submitted for merging.  You may also want to consider cooperating
> with the maintainer of the conflicting tree to minimise any particularly
> complex conflicts.
> 
> diff --cc mm/rmap.c
> index 8616308610b9,1f9b5a9cb121..000000000000
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@@ -1394,27 -1384,26 +1394,30 @@@ void folio_add_anon_rmap_pmd(struct fol
>    *
>    * Like folio_add_anon_rmap_*() but must only be called on *new* folios.
>    * This means the inc-and-test can be bypassed.
>  - * The folio does not have to be locked.
>  + * The folio doesn't necessarily need to be locked while it's exclusive
>  + * unless two threads map it concurrently. However, the folio must be
>  + * locked if it's shared.
>    *
>  - * If the folio is pmd-mappable, it is accounted as a THP.  As the folio
>  - * is new, it's assumed to be mapped exclusively by a single process.
>  + * If the folio is pmd-mappable, it is accounted as a THP.
>    */
>   void folio_add_new_anon_rmap(struct folio *folio, struct vm_area_struct *vma,
>  -		unsigned long address)
>  +		unsigned long address, rmap_t flags)
>   {
>  -	int nr = folio_nr_pages(folio);
>  +	const int nr = folio_nr_pages(folio);
>  +	const bool exclusive = flags & RMAP_EXCLUSIVE;
>  +	int nr_pmdmapped = 0;
>   
>   	VM_WARN_ON_FOLIO(folio_test_hugetlb(folio), folio);
>  +	VM_WARN_ON_FOLIO(!exclusive && !folio_test_locked(folio), folio);
>   	VM_BUG_ON_VMA(address < vma->vm_start ||
>   			address + (nr << PAGE_SHIFT) > vma->vm_end, vma);
> - 
> - 	if (!folio_test_swapbacked(folio))
> + 	/*
> + 	 * VM_DROPPABLE mappings don't swap; instead they're just dropped when
> + 	 * under memory pressure.
> + 	 */
>  -	if (!(vma->vm_flags & VM_DROPPABLE))
> ++	if (!folio_test_swapbacked(folio) && !(vma->vm_flags & VM_DROPPABLE))
>   		__folio_set_swapbacked(folio);
>  -	__folio_set_anon(folio, vma, address, true);
>  +	__folio_set_anon(folio, vma, address, exclusive);
>   
>   	if (likely(!folio_test_large(folio))) {
>   		/* increment count (starts at -1) */
> @@@ -1858,8 -1862,15 +1867,13 @@@ static bool try_to_unmap_one(struct fol
>   				 * discarded. Remap the page to page table.
>   				 */
>   				set_pte_at(mm, address, pvmw.pte, pteval);
> - 				folio_set_swapbacked(folio);
> + 				/*
> + 				 * Unlike MADV_FREE mappings, VM_DROPPABLE ones
> + 				 * never get swap backed on failure to drop.
> + 				 */
> + 				if (!(vma->vm_flags & VM_DROPPABLE))
> + 					folio_set_swapbacked(folio);
>  -				ret = false;
>  -				page_vma_mapped_walk_done(&pvmw);
>  -				break;
>  +				goto walk_abort;
>   			}
>   
>   			if (swap_duplicate(entry) < 0) {

This is now a conflict between the random tree and Linus' tree.

-- 
Cheers,
Stephen Rothwell

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