On Sun, Oct 06, 2019 at 05:45:59PM +0200, Christoph Hellwig wrote:
> Takes the xfs writeback code and copies it to iomap.c. A new structure
> with three methods is added as the abstraction from the generic
> writeback code to the file system. These methods are used to map
> blocks, submit an ioend, and cancel a page that encountered an error
> before it was added to an ioend.
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> [darrick: create the new iomap code, we'll delete the xfs code separately]
> Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
.....
> +static int
> +iomap_ioend_compare(void *priv, struct list_head *a, struct list_head *b)
> +{
> + struct iomap_ioend *ia, *ib;
> +
> + ia = container_of(a, struct iomap_ioend, io_list);
> + ib = container_of(b, struct iomap_ioend, io_list);
> + if (ia->io_offset < ib->io_offset)
> + return -1;
> + else if (ia->io_offset > ib->io_offset)
> + return 1;
> + return 0;
No need for the else here.
> +/*
> + * Test to see if we have an existing ioend structure that we could append to
> + * first, otherwise finish off the current ioend and start another.
> + */
> +static void
> +iomap_add_to_ioend(struct inode *inode, loff_t offset, struct page *page,
> + struct iomap_page *iop, struct iomap_writepage_ctx *wpc,
> + struct writeback_control *wbc, struct list_head *iolist)
> +{
> + sector_t sector = iomap_sector(&wpc->iomap, offset);
> + unsigned len = i_blocksize(inode);
> + unsigned poff = offset & (PAGE_SIZE - 1);
> + bool merged, same_page = false;
> +
> + if (!wpc->ioend ||
> + (wpc->iomap.flags & IOMAP_F_SHARED) !=
> + (wpc->ioend->io_flags & IOMAP_F_SHARED) ||
This second line of the comparison should be indented further as it
is a continuation of the the previous line's log statement, not a
unique logic statement by itself.
> + wpc->iomap.type != wpc->ioend->io_type ||
> + sector != bio_end_sector(wpc->ioend->io_bio) ||
> + offset != wpc->ioend->io_offset + wpc->ioend->io_size) {
> + if (wpc->ioend)
> + list_add(&wpc->ioend->io_list, iolist);
> + wpc->ioend = iomap_alloc_ioend(inode, wpc, offset, sector, wbc);
> + }
.....
> +static int
> +iomap_do_writepage(struct page *page, struct writeback_control *wbc, void *data)
> +{
> + struct iomap_writepage_ctx *wpc = data;
> + struct inode *inode = page->mapping->host;
> + pgoff_t end_index;
> + u64 end_offset;
> + loff_t offset;
> +
> + trace_iomap_writepage(inode, page, 0, 0);
> +
> + /*
> + * Refuse to write the page out if we are called from reclaim context.
> + *
> + * This avoids stack overflows when called from deeply used stacks in
> + * random callers for direct reclaim or memcg reclaim. We explicitly
> + * allow reclaim from kswapd as the stack usage there is relatively low.
> + *
> + * This should never happen except in the case of a VM regression so
> + * warn about it.
> + */
> + if (WARN_ON_ONCE((current->flags & (PF_MEMALLOC|PF_KSWAPD)) ==
> + PF_MEMALLOC))
> + goto redirty;
> +
> + /*
> + * Given that we do not allow direct reclaim to call us, we should
> + * never be called while in a filesystem transaction.
> + */
> + if (WARN_ON_ONCE(current->flags & PF_MEMALLOC_NOFS))
> + goto redirty;
Is this true for all expected callers of these functions rather than
just XFS? i.e. PF_MEMALLOC_NOFS is used by transactions in XFS to
prevent transaction context recursion, but other filesystems do not
do this..
FWIW, I can also see that this is going to cause us problems if high
level code starts using memalloc_nofs_save() and then calling
filemap_datawrite() and friends...
> +iomap_writepage(struct page *page, struct writeback_control *wbc,
> + struct iomap_writepage_ctx *wpc,
> + const struct iomap_writeback_ops *ops)
> +{
> + int ret;
> +
> + wpc->ops = ops;
> + ret = iomap_do_writepage(page, wbc, wpc);
> + if (!wpc->ioend)
> + return ret;
> + return iomap_submit_ioend(wpc, wpc->ioend, ret);
> +}
> +EXPORT_SYMBOL_GPL(iomap_writepage);
Can we kill ->writepage for iomap users, please? After all, we don't
mostly don't allow memory reclaim to do writeback of dirty pages,
and that's the only caller of ->writepage.
Cheers,
Dave.
--
Dave Chinner
david@xxxxxxxxxxxxx
