Re: [PATCH 09/26] mm: Provide a means of invalidation without using launder_folio

Jeff Layton
2024-04-15T11:41:07Z

On Thu, 2024-03-28 at 16:34 +0000, David Howells wrote:
> Implement a replacement for launder_folio. The key feature of
> invalidate_inode_pages2() is that it locks each folio individually, unmaps
> it to prevent mmap'd accesses interfering and calls the ->launder_folio()
> address_space op to flush it. This has problems: firstly, each folio is
> written individually as one or more small writes; secondly, adjacent folios
> cannot be added so easily into the laundry; thirdly, it's yet another op to
> implement.
>
> Instead, use the invalidate lock to cause anyone wanting to add a folio to
> the inode to wait, then unmap all the folios if we have mmaps, then,
> conditionally, use ->writepages() to flush any dirty data back and then
> discard all pages.
>
> The invalidate lock prevents ->read_iter(), ->write_iter() and faulting
> through mmap all from adding pages for the duration.
>
> Signed-off-by: David Howells <dhowells@redhat.com>
> cc: Matthew Wilcox <willy@infradead.org>
> cc: Miklos Szeredi <miklos@szeredi.hu>
> cc: Trond Myklebust <trond.myklebust@hammerspace.com>
> cc: Christoph Hellwig <hch@lst.de>
> cc: Andrew Morton <akpm@linux-foundation.org>
> cc: Alexander Viro <viro@zeniv.linux.org.uk>
> cc: Christian Brauner <brauner@kernel.org>
> cc: Jeff Layton <jlayton@kernel.org>
> cc: linux-mm@kvack.org
> cc: linux-fsdevel@vger.kernel.org
> cc: netfs@lists.linux.dev
> cc: v9fs@lists.linux.dev
> cc: linux-afs@lists.infradead.org
> cc: ceph-devel@vger.kernel.org
> cc: linux-cifs@vger.kernel.org
> cc: linux-nfs@vger.kernel.org
> cc: devel@lists.orangefs.org
> ---
> include/linux/pagemap.h | 1 +
> mm/filemap.c | 46 +++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 47 insertions(+)
>
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index 2df35e65557d..4eb3d4177a53 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -40,6 +40,7 @@ int filemap_fdatawait_keep_errors(struct address_space *mapping);
> int filemap_fdatawait_range(struct address_space *, loff_t lstart, loff_t lend);
> int filemap_fdatawait_range_keep_errors(struct address_space *mapping,
> loff_t start_byte, loff_t end_byte);
> +int filemap_invalidate_inode(struct inode *inode, bool flush);
>
> static inline int filemap_fdatawait(struct address_space *mapping)
> {
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 25983f0f96e3..087f685107a5 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -4134,6 +4134,52 @@ bool filemap_release_folio(struct folio *folio, gfp_t gfp)
> }
> EXPORT_SYMBOL(filemap_release_folio);
>
> +/**
> + * filemap_invalidate_inode - Invalidate/forcibly write back an inode's pagecache
> + * @inode: The inode to flush
> + * @flush: Set to write back rather than simply invalidate.
> + *
> + * Invalidate all the folios on an inode, possibly writing them back first.
> + * Whilst the operation is undertaken, the invalidate lock is held to prevent
> + * new folios from being installed.
> + */
> +int filemap_invalidate_inode(struct inode *inode, bool flush)
> +{
> + struct address_space *mapping = inode->i_mapping;
> +
> + if (!mapping || !mapping->nrpages)
> + goto out;
> +
> + /* Prevent new folios from being added to the inode. */
> + filemap_invalidate_lock(mapping);
> +
> + if (!mapping->nrpages)
> + goto unlock;
> +
> + unmap_mapping_pages(mapping, 0, ULONG_MAX, false);
> +
> + /* Write back the data if we're asked to. */
> + if (flush) {
> + struct writeback_control wbc = {
> + .sync_mode = WB_SYNC_ALL,
> + .nr_to_write = LONG_MAX,
> + .range_start = 0,
> + .range_end = LLONG_MAX,
> + };
> +
> + filemap_fdatawrite_wbc(mapping, &wbc);
> + }
> +
> + /* Wait for writeback to complete on all folios and discard. */
> + truncate_inode_pages_range(mapping, 0, LLONG_MAX);
> +
> +unlock:
> + filemap_invalidate_unlock(mapping);
> +out:
> + return filemap_check_errors(mapping);
> +}
> +EXPORT_SYMBOL(filemap_invalidate_inode);
> +
> #ifdef CONFIG_CACHESTAT_SYSCALL
> /**
> * filemap_cachestat() - compute the page cache statistics of a mapping
>
>

I'd have liked to have seen the first caller of this function too.
--
Jeff Layton <jlayton@kernel.org>