From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 67C3B39AD2A; Thu, 10 Sep 2026 21:05:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789074341; cv=none; b=KFA44qc96gk+kkWDPAtcKxxZG7RBHBHlC0AihPla1iCgcFgPwlZ8ROKjvqflD24PDQNdskUynLupJKOTMpKx4o6mOCsKlAINS1t/ZBmeNWigiFa8RbcpLrMar+hsXggWS8znSk6PQLljDgFrY3E63QKd9gR0WaXowHGaZk8yvu0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789074341; c=relaxed/simple; bh=eC1FWUYfMlG80WKxBlCNmNfp7ZQ52lIhs/luxQagGNk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=LYMgN4wc4BZywVrKO26sfDJfv9owZmIhWgc/8lG15NNggj6JyfMZnX+KTN8NbNH6KUnXaS6DPs4cIjtxRk56h/QEZEoHyO3sfsrmsC6dVP4/u4GZcLd8bYAvaSxj6gbfef6nVma5eNYQIPskscMgHZQb4SzwonCRtfSguyl7Kg8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=eMVAdsjn; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="eMVAdsjn" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EA7871F000FF; Thu, 10 Sep 2026 21:05:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789074340; bh=oLToX4EccLVtnhGx2Vc8M3u3T1qH7yOvY6cF4At7RK8=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=eMVAdsjnlliyWhH3OpkdXujTtNiigDS8c7DRnRcnAIebH2lnzAUn7CGlqjl3uXz0y s2ALMDFWBA/vymMAewgJcnnCue0nseOnWxIoiAGhV8fE786DdvJmyBvb+zHWePs8XR lF/fYrIuN9UJhL60bT5x2Fq9bJDI+mVu/yT4u1aXPqPqPf5DzIjhHhHx9SZoh9LVLO S79uttERoeDeu/vjm/SUOuF4gL0pYXMFFDStZZWSzMhfzYBwpaUD2hX0SAa/cZ2G43 X2y+psFM3rUo/eSavsDm38Ea70SOZJE5rt1/C6Z/69h1i0oG2cTvy1Dclr70hq/j/E qu/datkRNcZ7w== Message-ID: Date: Thu, 10 Sep 2026 23:05:29 +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 v2 09/26] mm/fbatch: restore mlock+munlock batching, without extra ref Content-Language: en-US To: Hugh Dickins , Andrew Morton Cc: Ackerley Tng , Alexander Viro , Alexandre Ghiti , Baolin Wang , Barry Song , Binbin Wu , Christian Brauner , Christoph Hellwig , Christoph Lameter , Claudio Imbrenda , David Hildenbrand , JP Kobryn , Jan Kara , Jens Axboe , Johannes Weiner , Kairui Song , Kiryl Shutsemau , Lance Yang , Leonardo Bras , Lorenzo Stoakes , Marcelo Tosatti , Matthew Wilcox , Mel Gorman , Miaohe Lin , Michal Hocko , Minchan Kim , Muchun Song , Oscar Salvador , Peter Zijlstra , Qi Zheng , Rik van Riel , Sebastian Andrzej Siewior , Shakeel Butt , Suren Baghdasaryan , Yang Shi , Yu Zhao , Zach O'Keefe , Zi Yan , linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <69ba633c-8fd5-1f4b-2e1e-b9b15b8946be@google.com> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/9/26 11:59, Hugh Dickins wrote: > Update mlock_folio(), munlock_folio() and their fbatch callouts and > helpers, to do folio_try_get()s at batch processing time, instead of > holding a folio reference all the while in mlock_fbatch: as in folio.c. > > But more interesting is the use of mod_mlock_count(), using try_cmpxchg() > to update folio->mlock_count safely when possible (now when on lru_add > fbatch as well as when unevictable). While __mlock_folio() is as hard to > think about as before, __munlock_folio() simpler because munlock_folio() > can adjust mlock_count itself without clear_lru() or lruvec lock, and so > do the folio_test_clear_mlocked() immediately for itself (without which > unevictable_pgs_cleared was likely to appear high, when it should be 0 > or low to indicate good mlock health). > > __munlock_folio() is safe for use even when the unreferenced folio has > been freed and reused. It appears that __mlock_folio() could affect a > folio which has been freed and reused, but only if it is reused as an > mlocked folio, in which case its mlock_count is spuriously incremented > (but usually a spurious munlock decrement will follow). How grave is > this? If unevictable_pgs_cleared remains low, not so bad. > > I've gone back and forth on whether to move mlock_fbatch and these > functions into mm/folio.c: for now they stay here in mm/mlock.c. > > Signed-off-by: Hugh Dickins > --- > mm/mlock.c | 147 +++++++++++++++++++++++++++++++---------------------- > 1 file changed, 86 insertions(+), 61 deletions(-) > > diff --git a/mm/mlock.c b/mm/mlock.c > index 2c690f18031e..1050010bbe0b 100644 > --- a/mm/mlock.c > +++ b/mm/mlock.c > @@ -58,6 +58,20 @@ EXPORT_SYMBOL(can_do_mlock); > * indicate the unevictable state. > */ > > +static long mod_mlock_count(struct folio *folio, long incdec) > +{ > + long mlock_count = READ_ONCE(folio->mlock_count); > + > + while (mlock_count & MLOCK_COUNT_0) { > + if (mlock_count + incdec < MLOCK_COUNT_0) > + return MLOCK_COUNT_0; > + if (try_cmpxchg(&folio->mlock_count, &mlock_count, > + mlock_count + incdec)) > + return mlock_count + incdec; > + } This never rereads folio->mlock_count to mlock_count inside the loop, so it can spin forever? (too late here for me to understand the rest today) > + return 0; > +} > +