linux-kernel - Re: [PATCH v4 35/36] mm: Convert do_set_pte() to set_pte

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Message-ID: <ZBho6Q6Xq/YqRmBT@casper.infradead.org>
Date:   Mon, 20 Mar 2023 14:08:41 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     "Yin, Fengwei" <fengwei.yin@...el.com>
Cc:     Ryan Roberts <ryan.roberts@....com>, linux-arch@...r.kernel.org,
        will@...nel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 35/36] mm: Convert do_set_pte() to set_pte_range()

On Mon, Mar 20, 2023 at 09:38:55PM +0800, Yin, Fengwei wrote:
> Thanks a lot to Ryan for helping to test the debug patch I made.
> 
> Ryan confirmed that the following change could fix the kernel build regression:
> diff --git a/mm/filemap.c b/mm/filemap.c
> index db86e459dde6..343d6ff36b2c 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -3557,7 +3557,7 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf,
> 
>                 ret |= filemap_map_folio_range(vmf, folio,
>                                 xas.xa_index - folio->index, addr, nr_pages);
> -               xas.xa_index += nr_pages;
> +               xas.xa_index += folio_test_large(folio) ? nr_pages : 0;
> 
>                 folio_unlock(folio);
>                 folio_put(folio);
> 
> I will make upstream-able change as "xas.xa_index += nr_pages - 1;"

Thanks to both of you!

Really, we shouldn't need to interfere with xas.xa_index at all.
Does this work?

diff --git a/mm/filemap.c b/mm/filemap.c
index 8e4f95c5b65a..e40c967dde5f 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -3420,10 +3420,10 @@ static bool filemap_map_pmd(struct vm_fault *vmf, struct folio *folio,
 	return false;
 }
 
-static struct folio *next_uptodate_page(struct folio *folio,
-				       struct address_space *mapping,
-				       struct xa_state *xas, pgoff_t end_pgoff)
+static struct folio *next_uptodate_folio(struct xa_state *xas,
+		struct address_space *mapping, pgoff_t end_pgoff)
 {
+	struct folio *folio = xas_next_entry(xas, end_pgoff);
 	unsigned long max_idx;
 
 	do {
@@ -3461,22 +3461,6 @@ static struct folio *next_uptodate_page(struct folio *folio,
 	return NULL;
 }
 
-static inline struct folio *first_map_page(struct address_space *mapping,
-					  struct xa_state *xas,
-					  pgoff_t end_pgoff)
-{
-	return next_uptodate_page(xas_find(xas, end_pgoff),
-				  mapping, xas, end_pgoff);
-}
-
-static inline struct folio *next_map_page(struct address_space *mapping,
-					 struct xa_state *xas,
-					 pgoff_t end_pgoff)
-{
-	return next_uptodate_page(xas_next_entry(xas, end_pgoff),
-				  mapping, xas, end_pgoff);
-}
-
 /*
  * Map page range [start_page, start_page + nr_pages) of folio.
  * start_page is gotten from start by folio_page(folio, start)
@@ -3552,7 +3536,7 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf,
 	int nr_pages = 0;
 
 	rcu_read_lock();
-	folio = first_map_page(mapping, &xas, end_pgoff);
+	folio = next_uptodate_folio(&xas, mapping, end_pgoff);
 	if (!folio)
 		goto out;
 
@@ -3574,11 +3558,11 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf,
 
 		ret |= filemap_map_folio_range(vmf, folio,
 				xas.xa_index - folio->index, addr, nr_pages);
-		xas.xa_index += nr_pages;
 
 		folio_unlock(folio);
 		folio_put(folio);
-	} while ((folio = next_map_page(mapping, &xas, end_pgoff)) != NULL);
+		folio = next_uptodate_folio(&xas, mapping, end_pgoff);
+	} while (folio);
 	pte_unmap_unlock(vmf->pte, vmf->ptl);
 out:
 	rcu_read_unlock();

> Ryan and I also identify some other changes needed. I am not sure how to
> integrate those changes to this series. Maybe an add-on patch after this
> series? Thanks.

Up to you; I'm happy to integrate fixup patches into the current series
or add on new ones.