diff mbox series

[4/9] shmem: remove shmem_get_partial_folio

Message ID 20230118094329.9553-5-hch@lst.de (mailing list archive)
State New, archived
Headers show
Series [1/9] mm: don't look at xarray value entries in split_huge_pages_in_file | expand

Commit Message

Christoph Hellwig Jan. 18, 2023, 9:43 a.m. UTC
Add a new SGP_FIND mode for shmem_get_partial_folio that works like
SGP_READ, but does not check i_size.  Use that instead of open coding
the page cache lookup in shmem_get_partial_folio.  Note that this is
a behavior change in that it reads in swap cache entries for offsets
outside i_size, possibly causing a little bit of extra work.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 include/linux/shmem_fs.h |  1 +
 mm/shmem.c               | 46 ++++++++++++----------------------------
 2 files changed, 15 insertions(+), 32 deletions(-)

Comments

Brian Foster Jan. 18, 2023, 1:57 p.m. UTC | #1
On Wed, Jan 18, 2023 at 10:43:24AM +0100, Christoph Hellwig wrote:
> Add a new SGP_FIND mode for shmem_get_partial_folio that works like
> SGP_READ, but does not check i_size.  Use that instead of open coding
> the page cache lookup in shmem_get_partial_folio.  Note that this is
> a behavior change in that it reads in swap cache entries for offsets
> outside i_size, possibly causing a little bit of extra work.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  include/linux/shmem_fs.h |  1 +
>  mm/shmem.c               | 46 ++++++++++++----------------------------
>  2 files changed, 15 insertions(+), 32 deletions(-)
> 
> diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
> index d09d54be4ffd99..7ba160ac066e5e 100644
> --- a/include/linux/shmem_fs.h
> +++ b/include/linux/shmem_fs.h
> @@ -105,6 +105,7 @@ enum sgp_type {
>  	SGP_CACHE,	/* don't exceed i_size, may allocate page */
>  	SGP_WRITE,	/* may exceed i_size, may allocate !Uptodate page */
>  	SGP_FALLOC,	/* like SGP_WRITE, but make existing page Uptodate */
> +	SGP_FIND,	/* like SGP_READ, but also read outside i_size */
>  };
>  
>  int shmem_get_folio(struct inode *inode, pgoff_t index, struct folio **foliop,
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 9e1015cbad29f9..e9500fea43a8dc 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -877,27 +877,6 @@ void shmem_unlock_mapping(struct address_space *mapping)
>  	}
>  }
>  
> -static struct folio *shmem_get_partial_folio(struct inode *inode, pgoff_t index)
> -{
> -	struct folio *folio;
> -
> -	/*
> -	 * At first avoid shmem_get_folio(,,,SGP_READ): that fails
> -	 * beyond i_size, and reports fallocated pages as holes.
> -	 */
> -	folio = __filemap_get_folio(inode->i_mapping, index,
> -					FGP_ENTRY | FGP_LOCK, 0);

This all seems reasonable to me at a glance, FWIW, but I am a little
curious why this wouldn't split up into two changes. I.e., switch this
over to filemap_get_entry() to minimally remove the FGP_ENTRY dependency
without a behavior change, then (perhaps after the next patch) introduce
SGP_FIND in a separate patch. That makes it easier to review and
potentially undo if it happens to pose a problem in the future. Hm?

Brian

> -	if (!xa_is_value(folio))
> -		return folio;
> -	/*
> -	 * But read a page back from swap if any of it is within i_size
> -	 * (although in some cases this is just a waste of time).
> -	 */
> -	folio = NULL;
> -	shmem_get_folio(inode, index, &folio, SGP_READ);
> -	return folio;
> -}
> -
>  /*
>   * Remove range of pages and swap entries from page cache, and free them.
>   * If !unfalloc, truncate or punch hole; if unfalloc, undo failed fallocate.
> @@ -957,7 +936,8 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend,
>  		goto whole_folios;
>  
>  	same_folio = (lstart >> PAGE_SHIFT) == (lend >> PAGE_SHIFT);
> -	folio = shmem_get_partial_folio(inode, lstart >> PAGE_SHIFT);
> +	folio = NULL;
> +	shmem_get_folio(inode, lstart >> PAGE_SHIFT, &folio, SGP_FIND);
>  	if (folio) {
>  		same_folio = lend < folio_pos(folio) + folio_size(folio);
>  		folio_mark_dirty(folio);
> @@ -971,14 +951,16 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend,
>  		folio = NULL;
>  	}
>  
> -	if (!same_folio)
> -		folio = shmem_get_partial_folio(inode, lend >> PAGE_SHIFT);
> -	if (folio) {
> -		folio_mark_dirty(folio);
> -		if (!truncate_inode_partial_folio(folio, lstart, lend))
> -			end = folio->index;
> -		folio_unlock(folio);
> -		folio_put(folio);
> +	if (!same_folio) {
> +		folio = NULL;
> +		shmem_get_folio(inode, lend >> PAGE_SHIFT, &folio, SGP_FIND);
> +		if (folio) {
> +			folio_mark_dirty(folio);
> +			if (!truncate_inode_partial_folio(folio, lstart, lend))
> +				end = folio->index;
> +			folio_unlock(folio);
> +			folio_put(folio);
> +		}
>  	}
>  
>  whole_folios:
> @@ -1900,7 +1882,7 @@ static int shmem_get_folio_gfp(struct inode *inode, pgoff_t index,
>  		if (folio_test_uptodate(folio))
>  			goto out;
>  		/* fallocated folio */
> -		if (sgp != SGP_READ)
> +		if (sgp != SGP_READ && sgp != SGP_FIND)
>  			goto clear;
>  		folio_unlock(folio);
>  		folio_put(folio);
> @@ -1911,7 +1893,7 @@ static int shmem_get_folio_gfp(struct inode *inode, pgoff_t index,
>  	 * SGP_NOALLOC: fail on hole, with NULL folio, letting caller fail.
>  	 */
>  	*foliop = NULL;
> -	if (sgp == SGP_READ)
> +	if (sgp == SGP_READ || sgp == SGP_FIND)
>  		return 0;
>  	if (sgp == SGP_NOALLOC)
>  		return -ENOENT;
> -- 
> 2.39.0
> 
>
Christoph Hellwig Jan. 18, 2023, 4:43 p.m. UTC | #2
On Wed, Jan 18, 2023 at 08:57:05AM -0500, Brian Foster wrote:
> This all seems reasonable to me at a glance, FWIW, but I am a little
> curious why this wouldn't split up into two changes. I.e., switch this
> over to filemap_get_entry() to minimally remove the FGP_ENTRY dependency
> without a behavior change, then (perhaps after the next patch) introduce
> SGP_FIND in a separate patch. That makes it easier to review and
> potentially undo if it happens to pose a problem in the future. Hm?

The minimal change to filemap_get_entry would require to add the
lock, check mapping and retry loop and thus add a fair amount of
code.  So I looked for ways to avoid that and came up with this
version.  But if there is a strong preference to first open code
the logic and then later consolidate it I could do that.
Brian Foster Jan. 18, 2023, 4:50 p.m. UTC | #3
On Wed, Jan 18, 2023 at 05:43:58PM +0100, Christoph Hellwig wrote:
> On Wed, Jan 18, 2023 at 08:57:05AM -0500, Brian Foster wrote:
> > This all seems reasonable to me at a glance, FWIW, but I am a little
> > curious why this wouldn't split up into two changes. I.e., switch this
> > over to filemap_get_entry() to minimally remove the FGP_ENTRY dependency
> > without a behavior change, then (perhaps after the next patch) introduce
> > SGP_FIND in a separate patch. That makes it easier to review and
> > potentially undo if it happens to pose a problem in the future. Hm?
> 
> The minimal change to filemap_get_entry would require to add the
> lock, check mapping and retry loop and thus add a fair amount of
> code.  So I looked for ways to avoid that and came up with this
> version.  But if there is a strong preference to first open code
> the logic and then later consolidate it I could do that.
> 

Ok. Not a strong preference from me. I don't think it's worth
complicating that much just to split up.

Brian
diff mbox series

Patch

diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index d09d54be4ffd99..7ba160ac066e5e 100644
--- a/include/linux/shmem_fs.h
+++ b/include/linux/shmem_fs.h
@@ -105,6 +105,7 @@  enum sgp_type {
 	SGP_CACHE,	/* don't exceed i_size, may allocate page */
 	SGP_WRITE,	/* may exceed i_size, may allocate !Uptodate page */
 	SGP_FALLOC,	/* like SGP_WRITE, but make existing page Uptodate */
+	SGP_FIND,	/* like SGP_READ, but also read outside i_size */
 };
 
 int shmem_get_folio(struct inode *inode, pgoff_t index, struct folio **foliop,
diff --git a/mm/shmem.c b/mm/shmem.c
index 9e1015cbad29f9..e9500fea43a8dc 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -877,27 +877,6 @@  void shmem_unlock_mapping(struct address_space *mapping)
 	}
 }
 
-static struct folio *shmem_get_partial_folio(struct inode *inode, pgoff_t index)
-{
-	struct folio *folio;
-
-	/*
-	 * At first avoid shmem_get_folio(,,,SGP_READ): that fails
-	 * beyond i_size, and reports fallocated pages as holes.
-	 */
-	folio = __filemap_get_folio(inode->i_mapping, index,
-					FGP_ENTRY | FGP_LOCK, 0);
-	if (!xa_is_value(folio))
-		return folio;
-	/*
-	 * But read a page back from swap if any of it is within i_size
-	 * (although in some cases this is just a waste of time).
-	 */
-	folio = NULL;
-	shmem_get_folio(inode, index, &folio, SGP_READ);
-	return folio;
-}
-
 /*
  * Remove range of pages and swap entries from page cache, and free them.
  * If !unfalloc, truncate or punch hole; if unfalloc, undo failed fallocate.
@@ -957,7 +936,8 @@  static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend,
 		goto whole_folios;
 
 	same_folio = (lstart >> PAGE_SHIFT) == (lend >> PAGE_SHIFT);
-	folio = shmem_get_partial_folio(inode, lstart >> PAGE_SHIFT);
+	folio = NULL;
+	shmem_get_folio(inode, lstart >> PAGE_SHIFT, &folio, SGP_FIND);
 	if (folio) {
 		same_folio = lend < folio_pos(folio) + folio_size(folio);
 		folio_mark_dirty(folio);
@@ -971,14 +951,16 @@  static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend,
 		folio = NULL;
 	}
 
-	if (!same_folio)
-		folio = shmem_get_partial_folio(inode, lend >> PAGE_SHIFT);
-	if (folio) {
-		folio_mark_dirty(folio);
-		if (!truncate_inode_partial_folio(folio, lstart, lend))
-			end = folio->index;
-		folio_unlock(folio);
-		folio_put(folio);
+	if (!same_folio) {
+		folio = NULL;
+		shmem_get_folio(inode, lend >> PAGE_SHIFT, &folio, SGP_FIND);
+		if (folio) {
+			folio_mark_dirty(folio);
+			if (!truncate_inode_partial_folio(folio, lstart, lend))
+				end = folio->index;
+			folio_unlock(folio);
+			folio_put(folio);
+		}
 	}
 
 whole_folios:
@@ -1900,7 +1882,7 @@  static int shmem_get_folio_gfp(struct inode *inode, pgoff_t index,
 		if (folio_test_uptodate(folio))
 			goto out;
 		/* fallocated folio */
-		if (sgp != SGP_READ)
+		if (sgp != SGP_READ && sgp != SGP_FIND)
 			goto clear;
 		folio_unlock(folio);
 		folio_put(folio);
@@ -1911,7 +1893,7 @@  static int shmem_get_folio_gfp(struct inode *inode, pgoff_t index,
 	 * SGP_NOALLOC: fail on hole, with NULL folio, letting caller fail.
 	 */
 	*foliop = NULL;
-	if (sgp == SGP_READ)
+	if (sgp == SGP_READ || sgp == SGP_FIND)
 		return 0;
 	if (sgp == SGP_NOALLOC)
 		return -ENOENT;