linux-kernel - Re: [RFC 06/23] mm: call xas_set_order() in replace_page_cache

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Date:   Fri, 15 Sep 2023 20:46:10 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Pankaj Raghav <kernel@...kajraghav.com>
Cc:     linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        p.raghav@...sung.com, david@...morbit.com, da.gomez@...sung.com,
        akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        djwong@...nel.org, linux-mm@...ck.org, chandan.babu@...cle.com,
        mcgrof@...nel.org, gost.dev@...sung.com
Subject: Re: [RFC 06/23] mm: call xas_set_order() in
 replace_page_cache_folio()

On Fri, Sep 15, 2023 at 08:38:31PM +0200, Pankaj Raghav wrote:
> From: Luis Chamberlain <mcgrof@...nel.org>
> 
> Call xas_set_order() in replace_page_cache_folio() for non hugetlb
> pages.

This function definitely should work without this patch.  What goes wrong?

> Signed-off-by: Luis Chamberlain <mcgrof@...nel.org>
> ---
>  mm/filemap.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 4dee24b5b61c..33de71bfa953 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -815,12 +815,14 @@ EXPORT_SYMBOL(file_write_and_wait_range);
>  void replace_page_cache_folio(struct folio *old, struct folio *new)
>  {
>  	struct address_space *mapping = old->mapping;
> +	unsigned int min_order = mapping_min_folio_order(mapping);
>  	void (*free_folio)(struct folio *) = mapping->a_ops->free_folio;
>  	pgoff_t offset = old->index;
>  	XA_STATE(xas, &mapping->i_pages, offset);
>  
>  	VM_BUG_ON_FOLIO(!folio_test_locked(old), old);
>  	VM_BUG_ON_FOLIO(!folio_test_locked(new), new);
> +	VM_BUG_ON_FOLIO(folio_order(new) != folio_order(old), new);
>  	VM_BUG_ON_FOLIO(new->mapping, new);
>  
>  	folio_get(new);
> @@ -829,6 +831,11 @@ void replace_page_cache_folio(struct folio *old, struct folio *new)
>  
>  	mem_cgroup_migrate(old, new);
>  
> +	if (!folio_test_hugetlb(new)) {
> +		VM_BUG_ON_FOLIO(folio_order(new) < min_order, new);
> +		xas_set_order(&xas, offset, folio_order(new));
> +	}
> +
>  	xas_lock_irq(&xas);
>  	xas_store(&xas, new);
>  
> -- 
> 2.40.1
>