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Received: from willy by casper.infradead.org with local (Exim 4.99.1 #2 (Red Hat Linux)) id 1wzvu2-0000000Ehny-3KzH; Fri, 28 Aug 2026 12:41:50 +0000 Date: Fri, 28 Aug 2026 13:41:50 +0100 From: Matthew Wilcox To: Amir Goldstein Cc: Yuan-Hao Hsu , Miklos Szeredi , linux-unionfs@vger.kernel.org, linux-kernel@vger.kernel.org, Andrew Morton , Lorenzo Stoakes , Vlastimil Babka , Jann Horn , David Hildenbrand , Linux MM , Christian Brauner , "zhangyi (F)" , tujinjiang@huawe.com Subject: Re: [PATCH] ovl: implement ->get_unmapped_area() Message-ID: References: <20260827170718.497-1-aa9736195201@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam11 X-Rspam-User: X-Stat-Signature: jn41jiuo5yhjp8pf8m7z93fecahasw4a X-Rspamd-Queue-Id: 0AB59120004 X-HE-Tag: 1787920920-238768 X-HE-Meta: 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 j/cHweWM G3VrIj1NCD46fzOZ40o68DLZRjEFEnhDvDELRR6t6Sg2Qo+icT5E57Wd1m0Ps1iNF6ppRsnI1r1gNxn9OzE9hZJLtCiT69NPJC8LRBTXOCLfj7xVthpi3wqAwDvTCN/T/w02aZw9P97COkteFElTmp4iSL/EbEhjSfGwu1gSKZknvQwo52gF7R8G4PNDIcFT57C2ZOjRqyzPtP2Tk03/cGCWaCYg1lTtKrE/LXs6oca8x+xWQV08sP0mrMcB7r/3bcK2jfWsGvvFjaQRE4ebKEGvcx+Pf0S0zkDq1J9xpmUHROR9oT/cVwu/efEOYdMyT9f6niteZxXGL9mPbSnEj8Wbhvw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Aug 28, 2026 at 02:23:11PM +0200, Amir Goldstein wrote: > Since mmap is going through backing_file_mmap() probably a good idea to > pass this method through a backing_file helper as well. > > But more importantly, adding MM people to this patch review, mainly the ones > that participated in the discussion over patch to fix similar issues > in 2024 [1]. > Most of the concerns in that patch seem to have been addressed (?) > > [1] https://lore.kernel.org/linux-unionfs/20241205143038.3260233-1-tujinjiang@huawei.com/ No, not at all. All this patch needs to be is: +++ b/fs/overlayfs/file.c @@ -657,6 +657,7 @@ const struct file_operations ovl_file_operations = { .fallocate = ovl_fallocate, .fadvise = ovl_fadvise, .flush = ovl_flush, + .get_unmapped_area = thp_get_unmapped_area, .splice_read = ovl_splice_read, .splice_write = ovl_splice_write, All this "oh we have to call the underlying filesystem's get_unmapepd_area" betrays a lack of understanding of the problem. And Lorenzo suggested this in the linked thread: https://lore.kernel.org/linux-unionfs/69b72e3d-b101-4641-9ce5-51346c93a98d@lucifer.local/