Re: [PATCH v10 24/25] fuse: Convert from readpages to readahead
On Wed, Mar 25, 2020 at 4:32 PM Matthew Wilcox 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
Re: [PATCH v10 24/25] fuse: Convert from readpages to readahead
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.
Re: [PATCH v10 24/25] fuse: Convert from readpages to readahead
On Wed, Mar 25, 2020 at 1:02 PM Matthew Wilcox 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
Re: [PATCH v10 24/25] fuse: Convert from readpages to readahead
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)
Re: [PATCH v10 24/25] fuse: Convert from readpages to readahead
On Mon, Mar 23, 2020 at 9:23 PM Matthew Wilcox wrote:
>
> From: "Matthew Wilcox (Oracle)"
>
> 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)
> Reviewed-by: Dave Chinner
> Reviewed-by: William Kucharski
> ---
> 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
