On Mon, Jul 02, 2018 at 08:58:11AM -0600, Christoph Hellwig wrote:
> After already supporting a simple implementation of buffered writes for
> the blocksize == PAGE_SIZE case in the last commit this adds full support
> even for smaller block sizes. There are three bits of per-block
> information in the buffer_head structure that really matter for the iomap
> read and write path:
>
> - uptodate status (BH_uptodate)
> - marked as currently under read I/O (BH_Async_Read)
> - marked as currently under write I/O (BH_Async_Write)
>
> Instead of having new per-block structures this now adds a per-page
> structure called struct iomap_page to track this information in a slightly
> different form:
>
> - a bitmap for the per-block uptodate status. For worst case of a 64k
> page size system this bitmap needs to contain 128 bits. For the
> typical 4k page size case it only needs 8 bits, although we still
> need a full unsigned long due to the way the atomic bitmap API works.
> - two atomic_t counters are used to track the outstanding read and write
> counts
>
> There is quite a bit of boilerplate code as the buffered I/O path uses
> various helper methods, but the actual code is very straight forward.
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
> fs/iomap.c | 279 ++++++++++++++++++++++++++++++++++++++----
> include/linux/iomap.h | 31 +++++
> 2 files changed, 289 insertions(+), 21 deletions(-)
>
> diff --git a/fs/iomap.c b/fs/iomap.c
> index 13cdcf33e6c0..ea1b1ba61ba3 100644
> --- a/fs/iomap.c
> +++ b/fs/iomap.c
...
> @@ -161,13 +295,13 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
> return PAGE_SIZE;
> }
>
> - /* we don't support blocksize < PAGE_SIZE quite yet. */
> - WARN_ON_ONCE(pos != page_offset(page));
> - WARN_ON_ONCE(plen != PAGE_SIZE);
> + iomap_adjust_read_range(inode, iop, &pos, length, &poff, &plen);
> + if (plen == 0)
> + goto done;
>
I think the i_size check confused me in the previous go around. It's
obviously clear to me now after the iomap zeroing issue and fix, but a
one-liner comment couldn't hurt for future reference:
/* zero post-eof blocks as the page may be mapped */
That nit aside, this looks good to me and survives my tests:
Reviewed-by: Brian Foster <bfoster@xxxxxxxxxx>
> if (iomap->type != IOMAP_MAPPED || pos >= i_size_read(inode)) {
> zero_user(page, poff, plen);
> - SetPageUptodate(page);
> + iomap_set_range_uptodate(page, poff, plen);
> goto done;
> }
>
> @@ -183,6 +317,14 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
> is_contig = true;
> }
>
> + /*
> + * If we start a new segment we need to increase the read count, and we
> + * need to do so before submitting any previous full bio to make sure
> + * that we don't prematurely unlock the page.
> + */
> + if (iop)
> + atomic_inc(&iop->read_count);
> +
> if (!ctx->bio || !is_contig || bio_full(ctx->bio)) {
> gfp_t gfp = mapping_gfp_constraint(page->mapping, GFP_KERNEL);
> int nr_vecs = (length + PAGE_SIZE - 1) >> PAGE_SHIFT;
> @@ -203,7 +345,13 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
>
> __bio_add_page(ctx->bio, page, plen, poff);
> done:
> - return plen;
> + /*
> + * Move the caller beyond our range so that it keeps making progress.
> + * For that we have to include any leading non-uptodate ranges, but
> + * we can skip trailing ones as they will be handled in the next
> + * iteration.
> + */
> + return pos - orig_pos + plen;
> }
>
> int
> @@ -214,8 +362,6 @@ iomap_readpage(struct page *page, const struct iomap_ops *ops)
> unsigned poff;
> loff_t ret;
>
> - WARN_ON_ONCE(page_has_buffers(page));
> -
> for (poff = 0; poff < PAGE_SIZE; poff += ret) {
> ret = iomap_apply(inode, page_offset(page) + poff,
> PAGE_SIZE - poff, 0, ops, &ctx,
> @@ -341,6 +487,84 @@ iomap_readpages(struct address_space *mapping, struct list_head *pages,
> }
> EXPORT_SYMBOL_GPL(iomap_readpages);
>
> +int
> +iomap_is_partially_uptodate(struct page *page, unsigned long from,
> + unsigned long count)
> +{
> + struct iomap_page *iop = to_iomap_page(page);
> + struct inode *inode = page->mapping->host;
> + unsigned first = from >> inode->i_blkbits;
> + unsigned last = (from + count - 1) >> inode->i_blkbits;
> + unsigned i;
> +
> + if (iop) {
> + for (i = first; i <= last; i++)
> + if (!test_bit(i, iop->uptodate))
> + return 0;
> + return 1;
> + }
> +
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(iomap_is_partially_uptodate);
> +
> +int
> +iomap_releasepage(struct page *page, gfp_t gfp_mask)
> +{
> + /*
> + * mm accommodates an old ext3 case where clean pages might not have had
> + * the dirty bit cleared. Thus, it can send actual dirty pages to
> + * ->releasepage() via shrink_active_list(), skip those here.
> + */
> + if (PageDirty(page) || PageWriteback(page))
> + return 0;
> + iomap_page_release(page);
> + return 1;
> +}
> +EXPORT_SYMBOL_GPL(iomap_releasepage);
> +
> +void
> +iomap_invalidatepage(struct page *page, unsigned int offset, unsigned int len)
> +{
> + /*
> + * If we are invalidating the entire page, clear the dirty state from it
> + * and release it to avoid unnecessary buildup of the LRU.
> + */
> + if (offset == 0 && len == PAGE_SIZE) {
> + WARN_ON_ONCE(PageWriteback(page));
> + cancel_dirty_page(page);
> + iomap_page_release(page);
> + }
> +}
> +EXPORT_SYMBOL_GPL(iomap_invalidatepage);
> +
> +#ifdef CONFIG_MIGRATION
> +int
> +iomap_migrate_page(struct address_space *mapping, struct page *newpage,
> + struct page *page, enum migrate_mode mode)
> +{
> + int ret;
> +
> + ret = migrate_page_move_mapping(mapping, newpage, page, NULL, mode, 0);
> + if (ret != MIGRATEPAGE_SUCCESS)
> + return ret;
> +
> + if (page_has_private(page)) {
> + ClearPagePrivate(page);
> + set_page_private(newpage, page_private(page));
> + set_page_private(page, 0);
> + SetPagePrivate(newpage);
> + }
> +
> + if (mode != MIGRATE_SYNC_NO_COPY)
> + migrate_page_copy(newpage, page);
> + else
> + migrate_page_states(newpage, page);
> + return MIGRATEPAGE_SUCCESS;
> +}
> +EXPORT_SYMBOL_GPL(iomap_migrate_page);
> +#endif /* CONFIG_MIGRATION */
> +
> static void
> iomap_write_failed(struct inode *inode, loff_t pos, unsigned len)
> {
> @@ -364,6 +588,7 @@ iomap_read_page_sync(struct inode *inode, loff_t block_start, struct page *page,
>
> if (iomap->type != IOMAP_MAPPED || block_start >= i_size_read(inode)) {
> zero_user_segments(page, poff, from, to, poff + plen);
> + iomap_set_range_uptodate(page, poff, plen);
> return 0;
> }
>
> @@ -379,21 +604,33 @@ static int
> __iomap_write_begin(struct inode *inode, loff_t pos, unsigned len,
> struct page *page, struct iomap *iomap)
> {
> + struct iomap_page *iop = iomap_page_create(inode, page);
> loff_t block_size = i_blocksize(inode);
> loff_t block_start = pos & ~(block_size - 1);
> loff_t block_end = (pos + len + block_size - 1) & ~(block_size - 1);
> - unsigned poff = block_start & (PAGE_SIZE - 1);
> - unsigned plen = min_t(loff_t, PAGE_SIZE - poff, block_end - block_start);
> - unsigned from = pos & (PAGE_SIZE - 1), to = from + len;
> -
> - WARN_ON_ONCE(i_blocksize(inode) < PAGE_SIZE);
> + unsigned from = pos & (PAGE_SIZE - 1), to = from + len, poff, plen;
> + int status = 0;
>
> if (PageUptodate(page))
> return 0;
> - if (from <= poff && to >= poff + plen)
> - return 0;
> - return iomap_read_page_sync(inode, block_start, page,
> - poff, plen, from, to, iomap);
> +
> + do {
> + iomap_adjust_read_range(inode, iop, &block_start,
> + block_end - block_start, &poff, &plen);
> + if (plen == 0)
> + break;
> +
> + if ((from > poff && from < poff + plen) ||
> + (to > poff && to < poff + plen)) {
> + status = iomap_read_page_sync(inode, block_start, page,
> + poff, plen, from, to, iomap);
> + if (status)
> + break;
> + }
> +
> + } while ((block_start += plen) < block_end);
> +
> + return status;
> }
>
> static int
> @@ -476,7 +713,7 @@ __iomap_write_end(struct inode *inode, loff_t pos, unsigned len,
> if (unlikely(copied < len && !PageUptodate(page))) {
> copied = 0;
> } else {
> - SetPageUptodate(page);
> + iomap_set_range_uptodate(page, pos & (PAGE_SIZE - 1), len);
> iomap_set_page_dirty(page);
> }
> return __generic_write_end(inode, pos, copied, page);
> @@ -812,7 +1049,7 @@ iomap_page_mkwrite_actor(struct inode *inode, loff_t pos, loff_t length,
> block_commit_write(page, 0, length);
> } else {
> WARN_ON_ONCE(!PageUptodate(page));
> - WARN_ON_ONCE(i_blocksize(inode) < PAGE_SIZE);
> + iomap_page_create(inode, page);
> }
>
> return length;
> diff --git a/include/linux/iomap.h b/include/linux/iomap.h
> index 5eb9ca8d7ce5..3555d54bf79a 100644
> --- a/include/linux/iomap.h
> +++ b/include/linux/iomap.h
> @@ -2,6 +2,9 @@
> #ifndef LINUX_IOMAP_H
> #define LINUX_IOMAP_H 1
>
> +#include <linux/atomic.h>
> +#include <linux/bitmap.h>
> +#include <linux/mm.h>
> #include <linux/types.h>
>
> struct address_space;
> @@ -98,12 +101,40 @@ struct iomap_ops {
> ssize_t written, unsigned flags, struct iomap *iomap);
> };
>
> +/*
> + * Structure allocate for each page when block size < PAGE_SIZE to track
> + * sub-page uptodate status and I/O completions.
> + */
> +struct iomap_page {
> + atomic_t read_count;
> + atomic_t write_count;
> + DECLARE_BITMAP(uptodate, PAGE_SIZE / 512);
> +};
> +
> +static inline struct iomap_page *to_iomap_page(struct page *page)
> +{
> + if (page_has_private(page))
> + return (struct iomap_page *)page_private(page);
> + return NULL;
> +}
> +
> ssize_t iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *from,
> const struct iomap_ops *ops);
> int iomap_readpage(struct page *page, const struct iomap_ops *ops);
> int iomap_readpages(struct address_space *mapping, struct list_head *pages,
> unsigned nr_pages, const struct iomap_ops *ops);
> int iomap_set_page_dirty(struct page *page);
> +int iomap_is_partially_uptodate(struct page *page, unsigned long from,
> + unsigned long count);
> +int iomap_releasepage(struct page *page, gfp_t gfp_mask);
> +void iomap_invalidatepage(struct page *page, unsigned int offset,
> + unsigned int len);
> +#ifdef CONFIG_MIGRATION
> +int iomap_migrate_page(struct address_space *mapping, struct page *newpage,
> + struct page *page, enum migrate_mode mode);
> +#else
> +#define iomap_migrate_page NULL
> +#endif
> int iomap_file_dirty(struct inode *inode, loff_t pos, loff_t len,
> const struct iomap_ops *ops);
> int iomap_zero_range(struct inode *inode, loff_t pos, loff_t len,
> --
> 2.18.0
>
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