[v10,24/25] fuse: Convert from readpages to readahead
diff mbox series

Message ID 20200323202259.13363-25-willy@infradead.org
State New
Headers show
Series
  • Change readahead API
Related show

Commit Message

Matthew Wilcox March 23, 2020, 8:22 p.m. UTC
From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

Use the new readahead operation in fuse.  Switching away from the
read_cache_pages() helper gets rid of an implicit call to put_page(),
so we can get rid of the get_page() call in fuse_readpages_fill().

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
---
 fs/fuse/file.c | 46 +++++++++++++++++++---------------------------
 1 file changed, 19 insertions(+), 27 deletions(-)

Comments

Miklos Szeredi March 25, 2020, 9:42 a.m. UTC | #1
On Mon, Mar 23, 2020 at 9:23 PM Matthew Wilcox <willy@infradead.org> wrote:
>
> From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
>
> Use the new readahead operation in fuse.  Switching away from the
> read_cache_pages() helper gets rid of an implicit call to put_page(),
> so we can get rid of the get_page() call in fuse_readpages_fill().
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> Reviewed-by: Dave Chinner <dchinner@redhat.com>
> Reviewed-by: William Kucharski <william.kucharski@oracle.com>
> ---
>  fs/fuse/file.c | 46 +++++++++++++++++++---------------------------
>  1 file changed, 19 insertions(+), 27 deletions(-)
>
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index 9d67b830fb7a..5749505bcff6 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -923,9 +923,8 @@ struct fuse_fill_data {
>         unsigned int max_pages;
>  };
>
> -static int fuse_readpages_fill(void *_data, struct page *page)
> +static int fuse_readpages_fill(struct fuse_fill_data *data, struct page *page)
>  {
> -       struct fuse_fill_data *data = _data;
>         struct fuse_io_args *ia = data->ia;
>         struct fuse_args_pages *ap = &ia->ap;
>         struct inode *inode = data->inode;
> @@ -941,10 +940,8 @@ static int fuse_readpages_fill(void *_data, struct page *page)
>                                         fc->max_pages);
>                 fuse_send_readpages(ia, data->file);
>                 data->ia = ia = fuse_io_alloc(NULL, data->max_pages);
> -               if (!ia) {
> -                       unlock_page(page);
> +               if (!ia)
>                         return -ENOMEM;
> -               }
>                 ap = &ia->ap;
>         }
>
> @@ -954,7 +951,6 @@ static int fuse_readpages_fill(void *_data, struct page *page)
>                 return -EIO;
>         }
>
> -       get_page(page);
>         ap->pages[ap->num_pages] = page;
>         ap->descs[ap->num_pages].length = PAGE_SIZE;
>         ap->num_pages++;
> @@ -962,37 +958,33 @@ static int fuse_readpages_fill(void *_data, struct page *page)
>         return 0;
>  }
>
> -static int fuse_readpages(struct file *file, struct address_space *mapping,
> -                         struct list_head *pages, unsigned nr_pages)
> +static void fuse_readahead(struct readahead_control *rac)
>  {
> -       struct inode *inode = mapping->host;
> +       struct inode *inode = rac->mapping->host;
>         struct fuse_conn *fc = get_fuse_conn(inode);
>         struct fuse_fill_data data;
> -       int err;
> +       struct page *page;
>
> -       err = -EIO;
>         if (is_bad_inode(inode))
> -               goto out;
> +               return;
>
> -       data.file = file;
> +       data.file = rac->file;
>         data.inode = inode;
> -       data.nr_pages = nr_pages;
> -       data.max_pages = min_t(unsigned int, nr_pages, fc->max_pages);
> -;
> +       data.nr_pages = readahead_count(rac);
> +       data.max_pages = min_t(unsigned int, data.nr_pages, fc->max_pages);
>         data.ia = fuse_io_alloc(NULL, data.max_pages);
> -       err = -ENOMEM;
>         if (!data.ia)
> -               goto out;
> +               return;
>
> -       err = read_cache_pages(mapping, pages, fuse_readpages_fill, &data);
> -       if (!err) {
> -               if (data.ia->ap.num_pages)
> -                       fuse_send_readpages(data.ia, file);
> -               else
> -                       fuse_io_free(data.ia);
> +       while ((page = readahead_page(rac))) {
> +               if (fuse_readpages_fill(&data, page) != 0)

Shouldn't this unlock + put page on error?

Otherwise looks good.

Thanks,
Miklos
Matthew Wilcox March 25, 2020, 12:02 p.m. UTC | #2
On Wed, Mar 25, 2020 at 10:42:56AM +0100, Miklos Szeredi wrote:
> > +       while ((page = readahead_page(rac))) {
> > +               if (fuse_readpages_fill(&data, page) != 0)
> 
> Shouldn't this unlock + put page on error?

We're certainly inconsistent between the two error exits from
fuse_readpages_fill().  But I think we can simplify the whole thing
... how does this look to you?

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 5749505bcff6..57ea9a364e62 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -915,76 +915,32 @@ static void fuse_send_readpages(struct fuse_io_args *ia, struct file *file)
 	fuse_readpages_end(fc, &ap->args, err);
 }
 
-struct fuse_fill_data {
-	struct fuse_io_args *ia;
-	struct file *file;
-	struct inode *inode;
-	unsigned int nr_pages;
-	unsigned int max_pages;
-};
-
-static int fuse_readpages_fill(struct fuse_fill_data *data, struct page *page)
-{
-	struct fuse_io_args *ia = data->ia;
-	struct fuse_args_pages *ap = &ia->ap;
-	struct inode *inode = data->inode;
-	struct fuse_conn *fc = get_fuse_conn(inode);
-
-	fuse_wait_on_page_writeback(inode, page->index);
-
-	if (ap->num_pages &&
-	    (ap->num_pages == fc->max_pages ||
-	     (ap->num_pages + 1) * PAGE_SIZE > fc->max_read ||
-	     ap->pages[ap->num_pages - 1]->index + 1 != page->index)) {
-		data->max_pages = min_t(unsigned int, data->nr_pages,
-					fc->max_pages);
-		fuse_send_readpages(ia, data->file);
-		data->ia = ia = fuse_io_alloc(NULL, data->max_pages);
-		if (!ia)
-			return -ENOMEM;
-		ap = &ia->ap;
-	}
-
-	if (WARN_ON(ap->num_pages >= data->max_pages)) {
-		unlock_page(page);
-		fuse_io_free(ia);
-		return -EIO;
-	}
-
-	ap->pages[ap->num_pages] = page;
-	ap->descs[ap->num_pages].length = PAGE_SIZE;
-	ap->num_pages++;
-	data->nr_pages--;
-	return 0;
-}
-
 static void fuse_readahead(struct readahead_control *rac)
 {
 	struct inode *inode = rac->mapping->host;
 	struct fuse_conn *fc = get_fuse_conn(inode);
-	struct fuse_fill_data data;
-	struct page *page;
 
 	if (is_bad_inode(inode))
 		return;
 
-	data.file = rac->file;
-	data.inode = inode;
-	data.nr_pages = readahead_count(rac);
-	data.max_pages = min_t(unsigned int, data.nr_pages, fc->max_pages);
-	data.ia = fuse_io_alloc(NULL, data.max_pages);
-	if (!data.ia)
-		return;
+	while (readahead_count(rac)) {
+		struct fuse_io_args *ia;
+		struct fuse_args_pages *ap;
+		unsigned int i, nr_pages;
 
-	while ((page = readahead_page(rac))) {
-		if (fuse_readpages_fill(&data, page) != 0)
+		nr_pages = min(readahead_count(rac), fc->max_pages);
+		ia = fuse_io_alloc(NULL, nr_pages);
+		if (!ia)
 			return;
+		ap = &ia->ap;
+		__readahead_batch(rac, ap->pages, nr_pages);
+		for (i = 0; i < nr_pages; i++) {
+			fuse_wait_on_page_writeback(inode, ap->pages[i]->index);
+			ap->descs[i].length = PAGE_SIZE;
+		}
+		ap->num_pages = nr_pages;
+		fuse_send_readpages(ia, rac->file);
 	}
-
-	if (data.ia->ap.num_pages)
-		fuse_send_readpages(data.ia, rac->file);
-	else
-		fuse_io_free(data.ia);
 }
 
 static ssize_t fuse_cache_read_iter(struct kiocb *iocb, struct iov_iter *to)
Miklos Szeredi March 25, 2020, 2:43 p.m. UTC | #3
On Wed, Mar 25, 2020 at 1:02 PM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Wed, Mar 25, 2020 at 10:42:56AM +0100, Miklos Szeredi wrote:
> > > +       while ((page = readahead_page(rac))) {
> > > +               if (fuse_readpages_fill(&data, page) != 0)
> >
> > Shouldn't this unlock + put page on error?
>
> We're certainly inconsistent between the two error exits from
> fuse_readpages_fill().  But I think we can simplify the whole thing
> ... how does this look to you?

Nice, overall.

>
> -       while ((page = readahead_page(rac))) {
> -               if (fuse_readpages_fill(&data, page) != 0)
> +               nr_pages = min(readahead_count(rac), fc->max_pages);

Missing fc->max_read clamp.

> +               ia = fuse_io_alloc(NULL, nr_pages);
> +               if (!ia)
>                         return;
> +               ap = &ia->ap;
> +               __readahead_batch(rac, ap->pages, nr_pages);

nr_pages = __readahead_batch(...)?

This will give consecutive pages, right?

Thanks,
Miklos
Matthew Wilcox March 25, 2020, 3:32 p.m. UTC | #4
On Wed, Mar 25, 2020 at 03:43:02PM +0100, Miklos Szeredi wrote:
> >
> > -       while ((page = readahead_page(rac))) {
> > -               if (fuse_readpages_fill(&data, page) != 0)
> > +               nr_pages = min(readahead_count(rac), fc->max_pages);
> 
> Missing fc->max_read clamp.

Yeah, I realised that.  I ended up doing ...

+       unsigned int i, max_pages, nr_pages = 0;
...
+       max_pages = min(fc->max_pages, fc->max_read / PAGE_SIZE);

> > +               ia = fuse_io_alloc(NULL, nr_pages);
> > +               if (!ia)
> >                         return;
> > +               ap = &ia->ap;
> > +               __readahead_batch(rac, ap->pages, nr_pages);
> 
> nr_pages = __readahead_batch(...)?

That's the other bug ... this was designed for btrfs which has a fixed-size
buffer.  But you want to dynamically allocate fuse_io_args(), so we need to
figure out the number of pages beforehand, which is a little awkward.  I've
settled on this for the moment:

        for (;;) {
               struct fuse_io_args *ia;
                struct fuse_args_pages *ap;

                nr_pages = readahead_count(rac) - nr_pages;
                if (nr_pages > max_pages)
                        nr_pages = max_pages;
                if (nr_pages == 0)
                        break;
                ia = fuse_io_alloc(NULL, nr_pages);
                if (!ia)
                        return;
                ap = &ia->ap;
                __readahead_batch(rac, ap->pages, nr_pages);
                for (i = 0; i < nr_pages; i++) {
                        fuse_wait_on_page_writeback(inode,
                                                    readahead_index(rac) + i);
                        ap->descs[i].length = PAGE_SIZE;
                }
                ap->num_pages = nr_pages;
                fuse_send_readpages(ia, rac->file);
        }

but I'm not entirely happy with that either.  Pondering better options.

> This will give consecutive pages, right?

readpages() was already being called with consecutive pages.  Several
filesystems had code to cope with the pages being non-consecutive, but
that wasn't how the core code worked; if there was a discontiguity it
would send off the pages that were consecutive and start a new batch.

__readahead_batch() can't return fewer than nr_pages, so you don't need
to check for that.
Miklos Szeredi March 25, 2020, 3:54 p.m. UTC | #5
On Wed, Mar 25, 2020 at 4:32 PM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Wed, Mar 25, 2020 at 03:43:02PM +0100, Miklos Szeredi wrote:
> > >
> > > -       while ((page = readahead_page(rac))) {
> > > -               if (fuse_readpages_fill(&data, page) != 0)
> > > +               nr_pages = min(readahead_count(rac), fc->max_pages);
> >
> > Missing fc->max_read clamp.
>
> Yeah, I realised that.  I ended up doing ...
>
> +       unsigned int i, max_pages, nr_pages = 0;
> ...
> +       max_pages = min(fc->max_pages, fc->max_read / PAGE_SIZE);
>
> > > +               ia = fuse_io_alloc(NULL, nr_pages);
> > > +               if (!ia)
> > >                         return;
> > > +               ap = &ia->ap;
> > > +               __readahead_batch(rac, ap->pages, nr_pages);
> >
> > nr_pages = __readahead_batch(...)?
>
> That's the other bug ... this was designed for btrfs which has a fixed-size
> buffer.  But you want to dynamically allocate fuse_io_args(), so we need to
> figure out the number of pages beforehand, which is a little awkward.  I've
> settled on this for the moment:
>
>         for (;;) {
>                struct fuse_io_args *ia;
>                 struct fuse_args_pages *ap;
>
>                 nr_pages = readahead_count(rac) - nr_pages;
>                 if (nr_pages > max_pages)
>                         nr_pages = max_pages;
>                 if (nr_pages == 0)
>                         break;
>                 ia = fuse_io_alloc(NULL, nr_pages);
>                 if (!ia)
>                         return;
>                 ap = &ia->ap;
>                 __readahead_batch(rac, ap->pages, nr_pages);
>                 for (i = 0; i < nr_pages; i++) {
>                         fuse_wait_on_page_writeback(inode,
>                                                     readahead_index(rac) + i);
>                         ap->descs[i].length = PAGE_SIZE;
>                 }
>                 ap->num_pages = nr_pages;
>                 fuse_send_readpages(ia, rac->file);
>         }
>
> but I'm not entirely happy with that either.  Pondering better options.

I think that's fine.   Note how the original code possibly
over-allocates the the page array, because it doesn't know the batch
size beforehand.  So this is already better.

>
> > This will give consecutive pages, right?
>
> readpages() was already being called with consecutive pages.  Several
> filesystems had code to cope with the pages being non-consecutive, but
> that wasn't how the core code worked; if there was a discontiguity it
> would send off the pages that were consecutive and start a new batch.
>
> __readahead_batch() can't return fewer than nr_pages, so you don't need
> to check for that.

That's far from obvious.

I'd put a WARN_ON at least to make document the fact.

Thanks,
Miklos

Patch
diff mbox series

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 9d67b830fb7a..5749505bcff6 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -923,9 +923,8 @@  struct fuse_fill_data {
 	unsigned int max_pages;
 };
 
-static int fuse_readpages_fill(void *_data, struct page *page)
+static int fuse_readpages_fill(struct fuse_fill_data *data, struct page *page)
 {
-	struct fuse_fill_data *data = _data;
 	struct fuse_io_args *ia = data->ia;
 	struct fuse_args_pages *ap = &ia->ap;
 	struct inode *inode = data->inode;
@@ -941,10 +940,8 @@  static int fuse_readpages_fill(void *_data, struct page *page)
 					fc->max_pages);
 		fuse_send_readpages(ia, data->file);
 		data->ia = ia = fuse_io_alloc(NULL, data->max_pages);
-		if (!ia) {
-			unlock_page(page);
+		if (!ia)
 			return -ENOMEM;
-		}
 		ap = &ia->ap;
 	}
 
@@ -954,7 +951,6 @@  static int fuse_readpages_fill(void *_data, struct page *page)
 		return -EIO;
 	}
 
-	get_page(page);
 	ap->pages[ap->num_pages] = page;
 	ap->descs[ap->num_pages].length = PAGE_SIZE;
 	ap->num_pages++;
@@ -962,37 +958,33 @@  static int fuse_readpages_fill(void *_data, struct page *page)
 	return 0;
 }
 
-static int fuse_readpages(struct file *file, struct address_space *mapping,
-			  struct list_head *pages, unsigned nr_pages)
+static void fuse_readahead(struct readahead_control *rac)
 {
-	struct inode *inode = mapping->host;
+	struct inode *inode = rac->mapping->host;
 	struct fuse_conn *fc = get_fuse_conn(inode);
 	struct fuse_fill_data data;
-	int err;
+	struct page *page;
 
-	err = -EIO;
 	if (is_bad_inode(inode))
-		goto out;
+		return;
 
-	data.file = file;
+	data.file = rac->file;
 	data.inode = inode;
-	data.nr_pages = nr_pages;
-	data.max_pages = min_t(unsigned int, nr_pages, fc->max_pages);
-;
+	data.nr_pages = readahead_count(rac);
+	data.max_pages = min_t(unsigned int, data.nr_pages, fc->max_pages);
 	data.ia = fuse_io_alloc(NULL, data.max_pages);
-	err = -ENOMEM;
 	if (!data.ia)
-		goto out;
+		return;
 
-	err = read_cache_pages(mapping, pages, fuse_readpages_fill, &data);
-	if (!err) {
-		if (data.ia->ap.num_pages)
-			fuse_send_readpages(data.ia, file);
-		else
-			fuse_io_free(data.ia);
+	while ((page = readahead_page(rac))) {
+		if (fuse_readpages_fill(&data, page) != 0)
+			return;
 	}
-out:
-	return err;
+
+	if (data.ia->ap.num_pages)
+		fuse_send_readpages(data.ia, rac->file);
+	else
+		fuse_io_free(data.ia);
 }
 
 static ssize_t fuse_cache_read_iter(struct kiocb *iocb, struct iov_iter *to)
@@ -3373,10 +3365,10 @@  static const struct file_operations fuse_file_operations = {
 
 static const struct address_space_operations fuse_file_aops  = {
 	.readpage	= fuse_readpage,
+	.readahead	= fuse_readahead,
 	.writepage	= fuse_writepage,
 	.writepages	= fuse_writepages,
 	.launder_page	= fuse_launder_page,
-	.readpages	= fuse_readpages,
 	.set_page_dirty	= __set_page_dirty_nobuffers,
 	.bmap		= fuse_bmap,
 	.direct_IO	= fuse_direct_IO,