From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 356701C69D for ; Tue, 12 May 2026 11:07:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778584043; cv=none; b=VY1e1Dkjduj20i9ft6I/CcFxdk7WBnYGwRPtPOZlwTbJdf36u9gwtjIVYfgWOIq6oVt2Lnj4vodxV8t9gyzq3XeOBMC/fNtADSkgSME6rHDEtQGPbJ9PL1349lScea+xGYsKlIlTAnbs2hHNaawlPCL54dryK1+b+EBvOCNUgfs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778584043; c=relaxed/simple; bh=57ogFlXCXaF1a1TezDYO8b80gCjSnt1NZ3GTKLJt/JE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=SEBKRbD2Zn5cBzAZueAO3ubdGyU/Wzuvd9UPSwEKiRIXDk5NzvrBs92O8RxKgJ/Juh/JxcsfUYYCIPyfP9SUc1ZynDVYiyEP0srJsrd+LUveLGU/iFS0kRKqIRY/yUfEfQ4VrnfYPHDjBBcT38FH8pg27aq8NlLyq2f1UTXczAM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=pErSm8eU; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="pErSm8eU" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 33080C2BCF5; Tue, 12 May 2026 11:07:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778584042; bh=57ogFlXCXaF1a1TezDYO8b80gCjSnt1NZ3GTKLJt/JE=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=pErSm8eUzMBKLoiqQ3o+ZC2Y1VLqi3F3ko7yg46V+XNADbrN3N1rBhGHzpOVxdbLu g2ivbpVppCIXQrje70P/jD5NlL978DxORCWNzYJBTW5v1fY2XACE1c2DdS1w7vWuCN yxP/YrCIC302cn1uccn/GnFQUs8DdLnpZUcprBFRyUJt+ikOHSwQqyemjFgmFYZJXz oDoNl6rRLJvwwnYO0oAQFvoHtSp95vQPaM3UlhtrM3oSTWFcH8XRMufPuCC4NiWXZW O0n0LyS4Ok8iTJcJ83nj+91ZmF5qQBmgC7npf9Xh1zBhhG6MBLX5wlrM5zteLuMySS oYo3Ojon4WUmA== Message-ID: Date: Tue, 12 May 2026 13:07:16 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] mm/shmem: add shmem_insert_folio() To: =?UTF-8?Q?Thomas_Hellstr=C3=B6m?= , intel-xe@lists.freedesktop.org Cc: Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Hugh Dickins , Baolin Wang , Brendan Jackman , Johannes Weiner , Zi Yan , Christian Koenig , Huang Rui , Matthew Auld , Matthew Brost , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , dri-devel@lists.freedesktop.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260512110339.6244-1-thomas.hellstrom@linux.intel.com> <20260512110339.6244-2-thomas.hellstrom@linux.intel.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20260512110339.6244-2-thomas.hellstrom@linux.intel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit > > +/** > + * undo_compound_page() - Reverse the effect of prep_compound_page(). > + * @page: The head page of a compound page to demote. > + * > + * Returns the pages to non-compound state as if prep_compound_page() > + * had never been called. split_page() must NOT have been called on > + * the compound page; tail refcounts must be 0. The caller must ensure > + * no other users hold references to the compound page. > + */ > +void undo_compound_page(struct page *page) > +{ > + unsigned int i, nr = 1U << compound_order(page); > + > + page[1].flags.f &= ~PAGE_FLAGS_SECOND; > + for (i = 1; i < nr; i++) { > + page[i].mapping = NULL; > + clear_compound_head(&page[i]); > + } > + ClearPageHead(page); > +} > + > static inline void set_buddy_order(struct page *page, unsigned int order) > { > set_page_private(page, order); > diff --git a/mm/shmem.c b/mm/shmem.c > index 3b5dc21b323c..45e80a74f77c 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -937,6 +937,111 @@ int shmem_add_to_page_cache(struct folio *folio, > return 0; > } > > +/** > + * shmem_insert_folio() - Insert an isolated folio into a shmem file. > + * @file: The shmem file created with shmem_file_setup(). > + * @folio: The folio to insert. Must be isolated (not on LRU), unlocked, > + * have exactly one reference (the caller's), have no page-table > + * mappings, and have folio->mapping == NULL. > + * @order: The allocation order of @folio. If @order > 0 and @folio is > + * not already a large (compound) folio, it will be promoted to a > + * compound folio of this order inside this function. This requires > + * the standard post-alloc state: head refcount == 1, tail > + * refcounts == 0 (i.e. split_page() must NOT have been called). > + * On failure the promotion is reversed and the folio is returned > + * to its original non-compound state. > + * @index: Page-cache index at which to insert. Must be aligned to > + * (1 << @order) and within the file's size. > + * @writeback: If true, attempt immediate writeback to swap after insertion. > + * Best-effort; failure is silently ignored. > + * @folio_gfp: The GFP flags to use for memory-cgroup charging. > + * > + * The folio is inserted zero-copy into the shmem page cache and placed on > + * the anon LRU, where it participates in normal kernel reclaim (written to > + * swap under memory pressure). Any previous content at @index is discarded. > + * On success the caller should release their reference with folio_put() and > + * track the (@file, @index) pair for later recovery via shmem_read_folio() > + * and release via shmem_truncate_range(). > + * > + * Return: 0 on success. On failure the folio is returned to its original > + * state and the caller retains ownership. > + */ > +int shmem_insert_folio(struct file *file, struct folio *folio, unsigned int order, > + pgoff_t index, bool writeback, gfp_t folio_gfp) > +{ > + struct address_space *mapping = file->f_mapping; > + struct inode *inode = mapping->host; > + bool promoted; > + long nr_pages; > + int ret; > + > + promoted = order > 0 && !folio_test_large(folio); > + if (promoted) > + prep_compound_page(&folio->page, order); > + nr_pages = folio_nr_pages(folio); > + > + VM_BUG_ON_FOLIO(folio_test_lru(folio), folio); > + VM_BUG_ON_FOLIO(folio_mapped(folio), folio); > + VM_BUG_ON_FOLIO(folio_test_swapcache(folio), folio); > + VM_BUG_ON_FOLIO(folio->mapping, folio); > + VM_BUG_ON(index != round_down(index, nr_pages)); No new VM_BUG_ON_FOLIO etc. But in general, pushing in random allocated pages into shmem, converting them to folios is not something I particularly enjoy seeing. -- Cheers, David