From: John Hubbard <jhubbard@nvidia.com>
To: Matthew Wilcox <willy@infradead.org>, <linux-fsdevel@vger.kernel.org>
Cc: linux-xfs@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-f2fs-devel@lists.sourceforge.net, cluster-devel@redhat.com,
linux-mm@kvack.org, ocfs2-devel@oss.oracle.com,
linux-ext4@vger.kernel.org, linux-erofs@lists.ozlabs.org,
linux-btrfs@vger.kernel.org
Subject: Re: [PATCH v7 09/24] mm: Put readahead pages in cache earlier
Date: Thu, 20 Feb 2020 19:19:58 -0800 [thread overview]
Message-ID: <5691442b-56c7-7b0d-d91b-275be52abb42@nvidia.com> (raw)
In-Reply-To: <20200219210103.32400-10-willy@infradead.org>
On 2/19/20 1:00 PM, Matthew Wilcox wrote:
> From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
>
> When populating the page cache for readahead, mappings that use
> ->readpages must populate the page cache themselves as the pages are
> passed on a linked list which would normally be used for the page cache's
> LRU. For mappings that use ->readpage or the upcoming ->readahead method,
> we can put the pages into the page cache as soon as they're allocated,
> which solves a race between readahead and direct IO. It also lets us
> remove the gfp argument from read_pages().
>
> Use the new readahead_page() API to implement the repeated calls to
> ->readpage(), just like most filesystems will. This iterator also
> supports huge pages, even though none of the filesystems have been
> converted to use them yet.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---
> include/linux/pagemap.h | 20 +++++++++++++++++
> mm/readahead.c | 48 +++++++++++++++++++++++++----------------
> 2 files changed, 49 insertions(+), 19 deletions(-)
>
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index 55fcea0249e6..4989d330fada 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -647,8 +647,28 @@ struct readahead_control {
> /* private: use the readahead_* accessors instead */
> pgoff_t _index;
> unsigned int _nr_pages;
> + unsigned int _batch_count;
> };
>
> +static inline struct page *readahead_page(struct readahead_control *rac)
> +{
> + struct page *page;
> +
> + BUG_ON(rac->_batch_count > rac->_nr_pages);
> + rac->_nr_pages -= rac->_batch_count;
> + rac->_index += rac->_batch_count;
> + rac->_batch_count = 0;
Is it intentional, to set rac->_batch_count twice (here, and below)? The
only reason I can see is if a caller needs to use ->_batch_count in the
"return NULL" case, which doesn't seem to come up...
> +
> + if (!rac->_nr_pages)
> + return NULL;
> +
> + page = xa_load(&rac->mapping->i_pages, rac->_index);
> + VM_BUG_ON_PAGE(!PageLocked(page), page);
> + rac->_batch_count = hpage_nr_pages(page);
> +
> + return page;
> +}
> +
> /* The number of pages in this readahead block */
> static inline unsigned int readahead_count(struct readahead_control *rac)
> {
> diff --git a/mm/readahead.c b/mm/readahead.c
> index 83df5c061d33..aaa209559ba2 100644
> --- a/mm/readahead.c
> +++ b/mm/readahead.c
> @@ -113,15 +113,14 @@ int read_cache_pages(struct address_space *mapping, struct list_head *pages,
>
> EXPORT_SYMBOL(read_cache_pages);
>
> -static void read_pages(struct readahead_control *rac, struct list_head *pages,
> - gfp_t gfp)
> +static void read_pages(struct readahead_control *rac, struct list_head *pages)
> {
> const struct address_space_operations *aops = rac->mapping->a_ops;
> + struct page *page;
> struct blk_plug plug;
> - unsigned page_idx;
>
> if (!readahead_count(rac))
> - return;
> + goto out;
>
> blk_start_plug(&plug);
>
> @@ -130,23 +129,23 @@ static void read_pages(struct readahead_control *rac, struct list_head *pages,
> readahead_count(rac));
> /* Clean up the remaining pages */
> put_pages_list(pages);
> - goto out;
> - }
> -
> - for (page_idx = 0; page_idx < readahead_count(rac); page_idx++) {
> - struct page *page = lru_to_page(pages);
> - list_del(&page->lru);
> - if (!add_to_page_cache_lru(page, rac->mapping, page->index,
> - gfp))
> + rac->_index += rac->_nr_pages;
> + rac->_nr_pages = 0;
> + } else {
> + while ((page = readahead_page(rac))) {
> aops->readpage(rac->file, page);
> - put_page(page);
> + put_page(page);
> + }
> }
>
> -out:
> blk_finish_plug(&plug);
>
> BUG_ON(!list_empty(pages));
> - rac->_nr_pages = 0;
> + BUG_ON(readahead_count(rac));
> +
> +out:
> + /* If we were called due to a conflicting page, skip over it */
Tiny documentation nit: What if we were *not* called due to a conflicting page?
(And what is a "conflicting page", in this context, btw?) The next line unconditionally
moves the index ahead, so the "if" part of the comment really confuses me.
> + rac->_index++;
> }
>
> /*
> @@ -165,9 +164,11 @@ void __do_page_cache_readahead(struct address_space *mapping,
> LIST_HEAD(page_pool);
> loff_t isize = i_size_read(inode);
> gfp_t gfp_mask = readahead_gfp_mask(mapping);
> + bool use_list = mapping->a_ops->readpages;
> struct readahead_control rac = {
> .mapping = mapping,
> .file = filp,
> + ._index = index,
> ._nr_pages = 0,
> };
> unsigned long i;
> @@ -184,6 +185,8 @@ void __do_page_cache_readahead(struct address_space *mapping,
> if (index + i > end_index)
> break;
>
> + BUG_ON(index + i != rac._index + rac._nr_pages);
> +
> page = xa_load(&mapping->i_pages, index + i);
> if (page && !xa_is_value(page)) {
> /*
> @@ -191,15 +194,22 @@ void __do_page_cache_readahead(struct address_space *mapping,
> * contiguous pages before continuing with the next
> * batch.
> */
> - read_pages(&rac, &page_pool, gfp_mask);
> + read_pages(&rac, &page_pool);
> continue;
> }
>
> page = __page_cache_alloc(gfp_mask);
> if (!page)
> break;
> - page->index = index + i;
> - list_add(&page->lru, &page_pool);
> + if (use_list) {
> + page->index = index + i;
> + list_add(&page->lru, &page_pool);
> + } else if (add_to_page_cache_lru(page, mapping, index + i,
> + gfp_mask) < 0) {
I still think you'll want to compare against !=0, rather than < 0, here.
> + put_page(page);
> + read_pages(&rac, &page_pool);
Doing a read_pages() in the error case is because...actually, I'm not sure yet.
Why do we do this? Effectively it's a retry?
> + continue;
> + }
> if (i == nr_to_read - lookahead_size)
> SetPageReadahead(page);
> rac._nr_pages++;
> @@ -210,7 +220,7 @@ void __do_page_cache_readahead(struct address_space *mapping,
> * uptodate then the caller will launch readpage again, and
> * will then handle the error.
> */
> - read_pages(&rac, &page_pool, gfp_mask);
> + read_pages(&rac, &page_pool);
> }
>
> /*
>
Didn't spot any actual errors, just mainly my own questions here. :)
thanks,
--
John Hubbard
NVIDIA
next prev parent reply other threads:[~2020-02-21 3:20 UTC|newest]
Thread overview: 76+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-19 21:00 [PATCH v7 00/23] Change readahead API Matthew Wilcox
2020-02-19 21:00 ` [PATCH v7 01/24] mm: Move readahead prototypes from mm.h Matthew Wilcox
2020-02-21 2:43 ` John Hubbard
2020-02-21 21:48 ` Matthew Wilcox
2020-02-22 0:15 ` John Hubbard
2020-02-24 21:32 ` Christoph Hellwig
2020-02-19 21:00 ` [PATCH v7 02/24] mm: Return void from various readahead functions Matthew Wilcox
2020-02-24 21:33 ` Christoph Hellwig
2020-02-19 21:00 ` [PATCH v7 03/24] mm: Ignore return value of ->readpages Matthew Wilcox
2020-02-19 21:00 ` [PATCH v7 04/24] mm: Move readahead nr_pages check into read_pages Matthew Wilcox
2020-02-20 14:36 ` Zi Yan
2020-02-21 4:24 ` John Hubbard
2020-02-24 21:34 ` Christoph Hellwig
2020-02-19 21:00 ` [PATCH v7 05/24] mm: Use readahead_control to pass arguments Matthew Wilcox
2020-02-24 21:36 ` Christoph Hellwig
2020-02-19 21:00 ` [PATCH v7 06/24] mm: Rename various 'offset' parameters to 'index' Matthew Wilcox
2020-02-21 2:21 ` John Hubbard
2020-02-21 3:27 ` John Hubbard
2020-02-19 21:00 ` [PATCH v7 07/24] mm: rename readahead loop variable to 'i' Matthew Wilcox
2020-02-19 21:00 ` [PATCH v7 08/24] mm: Remove 'page_offset' from readahead loop Matthew Wilcox
2020-02-21 2:48 ` John Hubbard
2020-02-24 21:37 ` Christoph Hellwig
2020-02-19 21:00 ` [PATCH v7 09/24] mm: Put readahead pages in cache earlier Matthew Wilcox
2020-02-21 3:19 ` John Hubbard [this message]
2020-02-21 3:43 ` Matthew Wilcox
2020-02-21 4:19 ` John Hubbard
2020-02-24 21:40 ` Christoph Hellwig
2020-02-19 21:00 ` [PATCH v7 10/24] mm: Add readahead address space operation Matthew Wilcox
2020-02-20 15:00 ` Zi Yan
2020-02-20 15:10 ` Matthew Wilcox
2020-02-21 4:30 ` John Hubbard
2020-02-24 21:41 ` Christoph Hellwig
2020-02-19 21:00 ` [PATCH v7 11/24] mm: Move end_index check out of readahead loop Matthew Wilcox
2020-02-21 3:50 ` John Hubbard
2020-02-21 15:35 ` Matthew Wilcox
2020-02-21 19:41 ` John Hubbard
2020-02-19 21:00 ` [PATCH v7 12/24] mm: Add page_cache_readahead_unbounded Matthew Wilcox
2020-02-24 21:53 ` [Cluster-devel] " Christoph Hellwig
2020-02-19 21:00 ` [PATCH v7 13/24] fs: Convert mpage_readpages to mpage_readahead Matthew Wilcox
2020-02-24 21:54 ` [Cluster-devel] " Christoph Hellwig
2020-02-19 21:00 ` [PATCH v7 14/24] btrfs: Convert from readpages to readahead Matthew Wilcox
2020-02-20 9:42 ` Johannes Thumshirn
2020-02-20 13:48 ` Matthew Wilcox
2020-02-20 15:46 ` Christoph Hellwig
2020-02-20 15:54 ` Matthew Wilcox
2020-02-20 15:57 ` Christoph Hellwig
2020-02-24 21:43 ` Christoph Hellwig
2020-02-24 21:54 ` Matthew Wilcox
2020-02-24 21:57 ` Christoph Hellwig
2020-02-19 21:00 ` [PATCH v7 15/24] erofs: Convert uncompressed files " Matthew Wilcox
2020-02-19 21:00 ` [PATCH v7 16/24] erofs: Convert compressed " Matthew Wilcox
2020-02-19 21:00 ` [PATCH v7 17/24] ext4: Convert " Matthew Wilcox
2020-02-19 21:00 ` [PATCH v7 18/24] ext4: Pass the inode to ext4_mpage_readpages Matthew Wilcox
2020-02-19 21:00 ` [PATCH v7 19/24] f2fs: Convert from readpages to readahead Matthew Wilcox
2020-02-19 21:00 ` [PATCH v7 20/24] fuse: " Matthew Wilcox
2020-02-19 21:01 ` [PATCH v7 21/24] iomap: Restructure iomap_readpages_actor Matthew Wilcox
2020-02-20 15:47 ` Christoph Hellwig
2020-02-20 16:24 ` Matthew Wilcox
2020-02-24 22:17 ` Christoph Hellwig
2020-02-25 1:49 ` Matthew Wilcox
2020-02-22 0:44 ` Darrick J. Wong
2020-02-22 1:54 ` Matthew Wilcox
2020-02-23 17:55 ` Darrick J. Wong
2020-02-19 21:01 ` [PATCH v7 22/24] iomap: Convert from readpages to readahead Matthew Wilcox
2020-02-20 15:49 ` Christoph Hellwig
2020-02-20 16:57 ` Matthew Wilcox
2020-02-22 1:00 ` Darrick J. Wong
2020-02-24 4:33 ` Matthew Wilcox
2020-02-24 16:52 ` Darrick J. Wong
2020-02-22 1:03 ` Darrick J. Wong
2020-02-22 1:09 ` Matthew Wilcox
2020-02-19 21:01 ` [PATCH v7 23/24] mm: Document why we don't set PageReadahead Matthew Wilcox
2020-02-19 21:01 ` [PATCH v7 24/24] mm: Use memalloc_nofs_save in readahead path Matthew Wilcox
2020-02-20 17:54 ` [PATCH v7 00/23] Change readahead API David Sterba
2020-02-20 22:39 ` Matthew Wilcox
2020-02-21 11:59 ` David Sterba
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=5691442b-56c7-7b0d-d91b-275be52abb42@nvidia.com \
--to=jhubbard@nvidia.com \
--cc=cluster-devel@redhat.com \
--cc=linux-btrfs@vger.kernel.org \
--cc=linux-erofs@lists.ozlabs.org \
--cc=linux-ext4@vger.kernel.org \
--cc=linux-f2fs-devel@lists.sourceforge.net \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=linux-xfs@vger.kernel.org \
--cc=ocfs2-devel@oss.oracle.com \
--cc=willy@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).