Re: [PATCH v3] filemap: optimize folio refount update in filemap_map_pages

[David Hildenbrand <david@redhat.com>]

On 04.09.25 15:27, Jinjiang Tu wrote:
> There are two meaningless folio refcount update for order0 folio in
> filemap_map_pages(). First, filemap_map_order0_folio() adds folio refcount
> after the folio is mapped to pte. And then, filemap_map_pages() drops a
> refcount grabbed by next_uptodate_folio(). We could remain the refcount
> unchanged in this case.
> 
> As Matthew metenioned in [1], it is safe to call folio_unlock() before
> calling folio_put() here, because the folio is in page cache with refcount
> held, and truncation will wait for the unlock.
> 
> Optimize filemap_map_folio_range() with the same method too.
> 
> With this patch, we can get 8% performance gain for lmbench testcase
> 'lat_pagefault -P 1 file' in order0 folio case, the size of file is 512M.
> 
> [1]: https://lore.kernel.org/all/aKcU-fzxeW3xT5Wv@casper.infradead.org/
> 
> Signed-off-by: Jinjiang Tu <tujinjiang@huawei.com>
> ---

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 
Cheers

David / dhildenb