From: Bean Huo <[email protected]>
Current generic_file_buffered_read() will break up the larger batches of pages
and read data in single page length in case of ra->ra_pages == 0. This patch is
to allow it to pass the batches of pages down to the device if the supported
maximum IO size >= the requested size.
Signed-off-by: Bean Huo <[email protected]>
---
mm/filemap.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)
diff --git a/mm/filemap.c b/mm/filemap.c
index 1aaea26556cc..0deec1897817 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2062,6 +2062,7 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb,
struct file *filp = iocb->ki_filp;
struct address_space *mapping = filp->f_mapping;
struct inode *inode = mapping->host;
+ struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
struct file_ra_state *ra = &filp->f_ra;
loff_t *ppos = &iocb->ki_pos;
pgoff_t index;
@@ -2098,9 +2099,14 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb,
if (!page) {
if (iocb->ki_flags & IOCB_NOIO)
goto would_block;
- page_cache_sync_readahead(mapping,
- ra, filp,
- index, last_index - index);
+
+ if (!ra->ra_pages && bdi->io_pages >= last_index - index)
+ __do_page_cache_readahead(mapping, filp, index,
+ last_index - index, 0);
+ else
+ page_cache_sync_readahead(mapping, ra, filp,
+ index,
+ last_index - index);
page = find_get_page(mapping, index);
if (unlikely(page == NULL))
goto no_cached_page;
--
2.17.1
On Fri, 4 Sep 2020 16:48:07 +0200 Bean Huo <[email protected]> wrote:
> From: Bean Huo <[email protected]>
>
> Current generic_file_buffered_read() will break up the larger batches of pages
> and read data in single page length in case of ra->ra_pages == 0. This patch is
> to allow it to pass the batches of pages down to the device if the supported
> maximum IO size >= the requested size.
>
> ...
>
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -2062,6 +2062,7 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb,
> struct file *filp = iocb->ki_filp;
> struct address_space *mapping = filp->f_mapping;
> struct inode *inode = mapping->host;
> + struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
> struct file_ra_state *ra = &filp->f_ra;
> loff_t *ppos = &iocb->ki_pos;
> pgoff_t index;
> @@ -2098,9 +2099,14 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb,
> if (!page) {
> if (iocb->ki_flags & IOCB_NOIO)
> goto would_block;
> - page_cache_sync_readahead(mapping,
> - ra, filp,
> - index, last_index - index);
> +
> + if (!ra->ra_pages && bdi->io_pages >= last_index - index)
> + __do_page_cache_readahead(mapping, filp, index,
> + last_index - index, 0);
> + else
> + page_cache_sync_readahead(mapping, ra, filp,
> + index,
> + last_index - index);
> page = find_get_page(mapping, index);
> if (unlikely(page == NULL))
> goto no_cached_page;
I assume this is a performance patch. What are the observed changes in
behaviour?
What is special about ->ra_pages==0? Wouldn't this optimization still
be valid if ->ra_pages==2?
Doesn't this defeat the purpose of having ->ra_pages==0?
On Fri, Sep 04, 2020 at 04:48:07PM +0200, Bean Huo wrote:
> From: Bean Huo <[email protected]>
>
> Current generic_file_buffered_read() will break up the larger batches of pages
> and read data in single page length in case of ra->ra_pages == 0. This patch is
> to allow it to pass the batches of pages down to the device if the supported
> maximum IO size >= the requested size.
At least ubifs and mtd seem to force ra_pages = 0 to disable read-ahead
entirely, so this seems intentional.
On Fri, 2020-09-04 at 11:09 -0700, Andrew Morton wrote:
> On Fri, 4 Sep 2020 16:48:07 +0200 Bean Huo <[email protected]>
> wrote:
>
> > From: Bean Huo <[email protected]>
> >
> > Current generic_file_buffered_read() will break up the larger
> > batches of pages
> > and read data in single page length in case of ra->ra_pages == 0.
> > This patch is
> > to allow it to pass the batches of pages down to the device if the
> > supported
> > maximum IO size >= the requested size.
> >
> > ...
> >
> > --- a/mm/filemap.c
> > +++ b/mm/filemap.c
> > @@ -2062,6 +2062,7 @@ ssize_t generic_file_buffered_read(struct
> > kiocb *iocb,
> > struct file *filp = iocb->ki_filp;
> > struct address_space *mapping = filp->f_mapping;
> > struct inode *inode = mapping->host;
> > + struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
> > struct file_ra_state *ra = &filp->f_ra;
> > loff_t *ppos = &iocb->ki_pos;
> > pgoff_t index;
> > @@ -2098,9 +2099,14 @@ ssize_t generic_file_buffered_read(struct
> > kiocb *iocb,
> > if (!page) {
> > if (iocb->ki_flags & IOCB_NOIO)
> > goto would_block;
> > - page_cache_sync_readahead(mapping,
> > - ra, filp,
> > - index, last_index - index);
> > +
> > + if (!ra->ra_pages && bdi->io_pages >=
> > last_index - index)
> > + __do_page_cache_readahead(mapping,
> > filp, index,
> > + last_index -
> > index, 0);
> > + else
> > + page_cache_sync_readahead(mapping, ra,
> > filp,
> > + index,
> > + last_index -
> > index);
> > page = find_get_page(mapping, index);
> > if (unlikely(page == NULL))
> > goto no_cached_page;
>
> I assume this is a performance patch. What are the observed changes
> in behaviour?
>
> What is special about ->ra_pages==0? Wouldn't this optimization
> still
> be valid if ->ra_pages==2?
>
> Doesn't this defeat the purpose of having ->ra_pages==0?
Hi Andrew
Sorry, I am still not quite understanding your above three questions.
Based on my shallow understanding, ra_pages is associated with
read_ahead_kb. Seems ra_pages controls the maximum read-ahead window
size, but it doesn't work when the requested size exceeds ra_pages.
If I set the read_ahead_kb to 0, also, as Christoph mentioned, MTD
forcibly sets ra_pages to 0. I think the intention is that only wants
to disable read-ahead, however, doesn't want
generic_file_buffered_read() to split the request and read data with
4KB chunk size separately.
Thanks,
Bean
On Fri, Sep 11, 2020 at 10:15:24AM +0200, Bean Huo wrote:
> > What is special about ->ra_pages==0? Wouldn't this optimization
> > still
> > be valid if ->ra_pages==2?
> >
> > Doesn't this defeat the purpose of having ->ra_pages==0?
>
>
> Hi Andrew
> Sorry, I am still not quite understanding your above three questions.
>
> Based on my shallow understanding, ra_pages is associated with
> read_ahead_kb. Seems ra_pages controls the maximum read-ahead window
> size, but it doesn't work when the requested size exceeds ra_pages.
>
> If I set the read_ahead_kb to 0, also, as Christoph mentioned, MTD
> forcibly sets ra_pages to 0. I think the intention is that only wants
> to disable read-ahead, however, doesn't want
> generic_file_buffered_read() to split the request and read data with
> 4KB chunk size separately.
They way I understood Richard this is intentional.
On Fri, 2020-09-11 at 10:47 +0100, Christoph Hellwig wrote:
> > > Doesn't this defeat the purpose of having ->ra_pages==0?
> >
> >
> > Hi Andrew
> > Sorry, I am still not quite understanding your above three
> > questions.
> >
> > Based on my shallow understanding, ra_pages is associated with
> > read_ahead_kb. Seems ra_pages controls the maximum read-ahead
> > window
> > size, but it doesn't work when the requested size exceeds
> > ra_pages.
> >
> > If I set the read_ahead_kb to 0, also, as Christoph mentioned, MTD
> > forcibly sets ra_pages to 0. I think the intention is that only
> > wants
> > to disable read-ahead, however, doesn't want
> > generic_file_buffered_read() to split the request and read data
> > with
> > 4KB chunk size separately.
>
> They way I understood Richard this is intentional.
Hi Christoph
Thanks. understood now, MTD expects this result. Even so, I think this
patch doesn't impact MTD because the flash-based FS only achieved the
readpage. Inside __do_page_cache_readahead will use mapping->a_ops-
>readpage to read data.
Thanks,
Bean
On Fri, 2020-09-11 at 10:47 +0100, Christoph Hellwig wrote:
> > Hi Andrew
> > Sorry, I am still not quite understanding your above three
> > questions.
> >
> > Based on my shallow understanding, ra_pages is associated with
> > read_ahead_kb. Seems ra_pages controls the maximum read-ahead
> > window
> > size, but it doesn't work when the requested size exceeds
> > ra_pages.
> >
> > If I set the read_ahead_kb to 0, also, as Christoph mentioned, MTD
> > forcibly sets ra_pages to 0. I think the intention is that only
> > wants
> > to disable read-ahead, however, doesn't want
> > generic_file_buffered_read() to split the request and read data
> > with
> > 4KB chunk size separately.
>
> They way I understood Richard this is intentional.
Hi Christoph
Thanks. understood now, MTD expects this result. Even so, I think this
patch doesn't impact MTD because the flash-based FS only achieved the
readpage. Inside __do_page_cache_readahead will use mapping->a_ops-
>readpage to read data.
Thanks,
Bean