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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 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 X-Rspamd-Server: rspam04 X-Rspam-User: X-Stat-Signature: jwx5m8wczqupdq9sr4c3x8xkyesqwer9 X-Rspamd-Queue-Id: DAEE480003 X-HE-Tag: 1789074341-801134 X-HE-Meta: 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 vqWa2iXg shIiroh4F020R5Bauj93DFDZ/NskuQkSVZeGXQTg6aajBH/j8SFUR7pf7NMccWaLZv9KJRInv7kulu6sPl/JVl0Wdteww4ny5J+za52QByTE5FNw1UnL1+2lGbtAjVPS4lmK2EqKSzjG/4wHhdnRTgMAShI0O9aOC69oHdoyGt3y/rbFFL7KLBUlGUsAYVEPUqDi+XIa99WbdPGeW3YBPJ12zPfCzIwEMn3FP5nZPZvHtiub+2/jkDj6d8160ENbyhosLVn+RMW4nlvSa3BElrAFZgpWV61q26kLwGclGqWrgRMn+YYznAqz/gz2t0+eMme/OluQ1cKZlPijkJLAfQ7BM1EErCgXm/yBaXpmH+039CI4= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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; > +} > +