1/2 splice: dont steal (485ddb4b) · Commits · 戴 / test

Stealing pages with splice is problematic because we cannot just insert an uptodate page into the pagecache and hope the filesystem can take care of it later. We also cannot just ClearPageUptodate, then hope prepare_write does not write anything into the page, because I don't think prepare_write gives that guarantee. Remove support for SPLICE_F_MOVE for now. If we really want to bring it back, we might be able to do so with a the new filesystem buffered write aops APIs I'm working on. If we really don't want to bring it back, then we should decide that sooner rather than later, and remove the flag and all the stealing infrastructure before anybody starts using it. Signed-off-by:

Nick Piggin <npiggin@suse.de> Signed-off-by:

Jens Axboe <jens.axboe@oracle.com>

fs/splice.c

+38 −63

Original line number	Diff line number	Diff line
		@@ -576,30 +576,6 @@ static int pipe_to_file(struct pipe_inode_info pipe, struct pipe_buffer buf,
		if (this_len + offset > PAGE_CACHE_SIZE)
		this_len = PAGE_CACHE_SIZE - offset;

		/*
		* Reuse buf page, if SPLICE_F_MOVE is set and we are doing a full
		* page.
		*/
		if ((sd->flags & SPLICE_F_MOVE) && this_len == PAGE_CACHE_SIZE) {
		/*
		* If steal succeeds, buf->page is now pruned from the
		* pagecache and we can reuse it. The page will also be
		* locked on successful return.
		*/
		if (buf->ops->steal(pipe, buf))
		goto find_page;

		page = buf->page;
		if (add_to_page_cache(page, mapping, index, GFP_KERNEL)) {
		unlock_page(page);
		goto find_page;
		}

		page_cache_get(page);

		if (!(buf->flags & PIPE_BUF_FLAG_LRU))
		lru_cache_add(page);
		} else {
		find_page:
		page = find_lock_page(mapping, index);
		if (!page) {
		@@ -646,7 +622,6 @@ find_page:
		} else
		SetPageUptodate(page);
		}
		}

		ret = mapping->a_ops->prepare_write(file, page, offset, offset+this_len);
		if (unlikely(ret)) {

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