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 172793C5DB6; Mon, 11 May 2026 13:03:18 +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=1778504599; cv=none; b=TUj4297aV9y4rmrktK9JWg1lSTvaFMnZlh/QDBw4Tc039kbQmaDu1mwOwREcqmzLhJCBpnWPtLBTj+hmLc8b6rJ97j33t8tRaxl1Yyh18D0tXz1em4hRpT0NSs2g/cNb1FvMxauBEahuGLf0R52Io9c8fs31/VsdK+4jkZ5CObg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778504599; c=relaxed/simple; bh=kQwSfNCCLbUhti9udnSk7pt8oY35FAkzLyI7ofDZFwg=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=R8dSdc9snEGoPKrreOr+enNjxboo5Wy1adlOskAxHYNvbHmY6jVKtVbODriTnkwD7HdTeKl3ER+3uAxGBxWSBMHc05IOFjmGlp8zm6qI0HZPE5SeIVZha0nMWeNciKpyE+qk50RmLlGM2d2iMD8p7R9dNzDVKoanV5Ata+DKmrc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=uMdWgIVZ; 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="uMdWgIVZ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 830B2C2BCF7; Mon, 11 May 2026 13:03:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778504598; bh=kQwSfNCCLbUhti9udnSk7pt8oY35FAkzLyI7ofDZFwg=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=uMdWgIVZkHHB8pLI8a6wy8l2UtNjohCfS4udur4TYvZI+6hgM/SCtu3TMmbt8W1Oq 9/7BqjCUhPdbLlhv9AZIL8bcTT0c0lJgQkjCmHghkh6p7C5lrFp84dFqA7tLaqVyrC II41nrIt02dHlHV9sOsvZHjRsMWz97TpDCVOIMRsdkOOpqgaVeeCSTUK2YUsOIBEnh CbpQkdTELCzO4rdWW5Vn3+7jOiKiaLqiyjskP3xRe5+chEhnqFiYBsey5tvNGscfZa uzIAtCR5mJoeV3TVdj2Yo0mHwpJDSq8kYREQso4SIsMHQTACS+z1TqLsMKBp48llkS AqktpPLfYjMAg== Message-ID: <24edd9d6-99f2-4d3d-83eb-69b406f4a9a0@kernel.org> Date: Mon, 11 May 2026 15:03:14 +0200 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 4/5] mm: swap: fall back to order-0 after large swapin races To: fujunjie , Andrew Morton , Chris Li , Kairui Song , Johannes Weiner , Nhat Pham , Yosry Ahmed Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, Jonathan Corbet , Ryan Roberts , Barry Song , Baolin Wang , Chengming Zhou , Baoquan He , Lorenzo Stoakes References: From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 5/8/26 22:20, fujunjie wrote: > swapin_folio() documents that a large folio insertion race returns NULL > so the caller can fall back to order-0 swapin. do_swap_page() currently > turns that NULL into VM_FAULT_OOM if the PTE is unchanged, which is > harsher than necessary and gets in the way of rejecting large folio > ranges for backend reasons. > > Move the synchronous swapin sequence into a helper and retry with an > order-0 folio when a large folio cannot be inserted into the swap cache. > Count the event as an mTHP swapin fallback before dropping the failed > large allocation. > > Signed-off-by: fujunjie > --- > mm/memory.c | 50 +++++++++++++++++++++++++++++++++++++++----------- > 1 file changed, 39 insertions(+), 11 deletions(-) > > diff --git a/mm/memory.c b/mm/memory.c > index ea6568571131..84e3b77b8293 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -4757,6 +4757,44 @@ static struct folio *alloc_swap_folio(struct vm_fault *vmf) > } > #endif /* CONFIG_TRANSPARENT_HUGEPAGE */ > > +static struct folio *swapin_synchronous_folio(swp_entry_t entry, > + struct vm_fault *vmf) > +{ > + struct folio *swapcache, *folio; > + bool large; > + int order; > + > + folio = alloc_swap_folio(vmf); > + if (!folio) > + return NULL; > + > + large = folio_test_large(folio); > + order = folio_order(folio); > + > + /* > + * folio is charged, so swapin can only fail due to raced swapin and > + * return NULL. > + */ > + swapcache = swapin_folio(entry, folio); > + if (swapcache == folio) > + return folio; > + > + if (!swapcache && large) > + count_mthp_stat(order, MTHP_STAT_SWPIN_FALLBACK); > + folio_put(folio); > + if (swapcache || !large) > + return swapcache; > + > + folio = __alloc_swap_folio(vmf); > + if (!folio) > + return NULL; > + > + swapcache = swapin_folio(entry, folio); > + if (swapcache != folio) > + folio_put(folio); > + return swapcache; > +} > + > /* Sanity check that a folio is fully exclusive */ > static void check_swap_exclusive(struct folio *folio, swp_entry_t entry, > unsigned int nr_pages) > @@ -4860,17 +4898,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) > swap_update_readahead(folio, vma, vmf->address); > if (!folio) { > if (data_race(si->flags & SWP_SYNCHRONOUS_IO)) { > - folio = alloc_swap_folio(vmf); > - if (folio) { > - /* > - * folio is charged, so swapin can only fail due > - * to raced swapin and return NULL. > - */ > - swapcache = swapin_folio(entry, folio); > - if (swapcache != folio) > - folio_put(folio); > - folio = swapcache; > - } > + folio = swapin_synchronous_folio(entry, vmf); > } else { > folio = swapin_readahead(entry, GFP_HIGHUSER_MOVABLE, vmf); > } There are some upcoming changes with: https://lore.kernel.org/r/20260421-swap-table-p4-v3-5-2f23759a76bc@tencent.com All the of that logic you have in swapin_synchronous_folio() should ideally not go into memory.c, but into some swap specific code. But https://lore.kernel.org/r/20260421-swap-table-p4-v3-0-2f23759a76bc@tencent.com Already changes a lot of that. -- Cheers, David