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Date:   Fri, 16 Jul 2021 14:47:35 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Christoph Hellwig <hch@infradead.org>
Cc:     Gao Xiang <hsiangkao@linux.alibaba.com>,
        linux-erofs@lists.ozlabs.org, linux-fsdevel@vger.kernel.org,
        LKML <linux-kernel@vger.kernel.org>,
        "Darrick J. Wong" <djwong@kernel.org>, Chao Yu <chao@kernel.org>,
        Liu Bo <bo.liu@linux.alibaba.com>,
        Joseph Qi <joseph.qi@linux.alibaba.com>,
        Liu Jiang <gerry@linux.alibaba.com>,
        Andreas Gruenbacher <agruenba@redhat.com>
Subject: Re: [PATCH 1/2] iomap: support tail packing inline read
Message-ID: <YPGN97vWokqkWSZn@casper.infradead.org>
References: <20210716050724.225041-1-hsiangkao@linux.alibaba.com>
 <20210716050724.225041-2-hsiangkao@linux.alibaba.com>
 <YPFPDS5ktWJEUKTo@infradead.org>
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On Fri, Jul 16, 2021 at 10:19:09AM +0100, Christoph Hellwig wrote:
>  static void
>  iomap_read_inline_data(struct inode *inode, struct page *page,
> -		struct iomap *iomap)
> +		struct iomap *iomap, loff_t pos, unsigned int size)
>  {
> -	size_t size = i_size_read(inode);
> +	unsigned int block_aligned_size = round_up(size, i_blocksize(inode));
> +	unsigned int poff = offset_in_page(pos);
>  	void *addr;
>  
> -	if (PageUptodate(page))
> -		return;
> -
> -	BUG_ON(page_has_private(page));
> -	BUG_ON(page->index);
> +	/* make sure that inline_data doesn't cross page boundary */
>  	BUG_ON(size > PAGE_SIZE - offset_in_page(iomap->inline_data));
> +	BUG_ON(size != i_size_read(inode) - pos);
>  
>  	addr = kmap_atomic(page);
> -	memcpy(addr, iomap->inline_data, size);
> -	memset(addr + size, 0, PAGE_SIZE - size);
> +	memcpy(addr + poff, iomap->inline_data - iomap->offset + pos, size);
> +	memset(addr + poff + size, 0, block_aligned_size - size);
>  	kunmap_atomic(addr);
> -	SetPageUptodate(page);
> +
> +	iomap_set_range_uptodate(page, poff, block_aligned_size);
>  }

This should be relatively straightforward to port to folios.
I think it looks something like this ...

@@ -211,23 +211,18 @@ struct iomap_readpage_ctx {
 };

 static void iomap_read_inline_data(struct inode *inode, struct folio *folio,
-               struct iomap *iomap)
+               struct iomap *iomap, loff_t pos, size_t size)
 {
-       size_t size = i_size_read(inode);
        void *addr;
+       size_t offset = offset_in_folio(folio, pos);

-       if (folio_test_uptodate(folio))
-               return;
+       BUG_ON(size != i_size_read(inode) - pos);

-       BUG_ON(folio->index);
-       BUG_ON(folio_multi(folio));
-       BUG_ON(size > PAGE_SIZE - offset_in_page(iomap->inline_data));
-
-       addr = kmap_local_folio(folio, 0);
+       addr = kmap_local_folio(folio, offset);
        memcpy(addr, iomap->inline_data, size);
        memset(addr + size, 0, PAGE_SIZE - size);
        kunmap_local(addr);
-       folio_mark_uptodate(folio);
+       iomap_set_range_uptodate(folio, to_iomap_page(folio), pos, size);
 }

> -	if (iomap->type == IOMAP_INLINE) {
> -		WARN_ON_ONCE(pos);
> -		iomap_read_inline_data(inode, page, iomap);
> -		return PAGE_SIZE;
> -	}
> +	if (iomap->type == IOMAP_INLINE && !pos)
> +		WARN_ON_ONCE(to_iomap_page(page) != NULL);
> +	else
> +		iop = iomap_page_create(inode, page);

This WARN_ON doesn't make sense to me.  If a file contains bytes 0-2047
that are !INLINE and then bytes 2048-2050 that are INLINE, we're going
to trigger it.  Perhaps just make this:

	if (iomap->type != IOMAP_INLINE || pos)
		iop = iomap_page_create(inode, page);