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b=k7Z5niTt7xai93ANTmHBXk/cNl/JwAUqSQsSU/IV53pXiJwa0lPrt+4i0KRd+RRdN g6IL9KhSNTJ8yTLeyZXeQ68jcMAgqeBYiuSNJJjMEHLOGhqs7HCkfUtfRI9oO+qpOK 4VJGqm8nL4vVYUxZ9VHwYX8EUczxXB+IKsD4FRlMFmgihyTXFKa46iDz+OuHMjiIMg xIRCgCi2HdHATCpL17lS3hUpZb+D9fl0AcR+8lW7hn9rDC86QCJVUjpIonY1dqc/B0 RXwXa+9MA00B0s/07AimaLzJl+FpnUIt9IgSaX/NwYJOW4Ukv7QaqMbhHY4JAum3W/ ZIf+y0Xx1qCIA== Message-ID: Date: Thu, 27 Aug 2026 19:35:54 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 02/25] mm/fbatch: allow folios_put_refs() to skip xa_is_value() entries To: Hugh Dickins , Andrew Morton Cc: Ackerley Tng , Alexander Viro , Baolin Wang , Barry Song , Binbin Wu , Christian Brauner , Christoph Hellwig , Christoph Lameter , Claudio Imbrenda , JP Kobryn , Jan Kara , 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 , Vlastimil Babka , 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: <14a16945-529b-8bc0-ab38-3ea97e54e223@google.com> <44c7773e-5806-d24a-83c9-f39b3a134138@google.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 0A057180009 X-Stat-Signature: kfb68f6a7z6dckwaw75ksauocgjz7a7k X-HE-Tag: 1787852167-301156 X-HE-Meta: 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 RIH6ErZX dIlElPEBT0g/pumx8Bi/2MyrC+ADhF53Lij56HfubbttLqquGvmGSsbKc47edeRBfQiYn8Vdj48wewYPOTPwyqLHRkx1pmRsTGrGG11FqOus5A0EpRQRvkWiMJdMmVD12y9P9iJBhPVYKYNzqrvFht5vjGZpksSgI0vY9oMHIqgIpJTqclzPVMYS5DmSu418jEpd8jGnc2VkbhtkiDD9EAOPCtexoHGmCLgVuB434ChEb1+p5OTtPkXy1vNQmNAfg9wrK5WLrIt2mtMtR9Bvr4TwpiVPbQYLxA0UUojmpcyTcYeXBlIYrKolrPMb+04toPg4NZb4ResWkK+7qg61etrq8+YaxBhNhCF29Cd3mAqYL2gUHdz0Nl2/KcT4mFwaDsqVNjYqkT3ZuftPkeoqYItp5DNgBnt8Ec9Rpa43qHhY2MqY= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 8/24/26 15:55, Hugh Dickins wrote: > Let folios_put_refs() (hence folio_batch_release()) skip xa_is_value() > entries, and therefore remove unneeded folio_batch_remove_exceptionals(). > > It made some sense when introduced in 3.1 for shmem swap entries only, > but workingset shadows popularized exceptional entries in 3.15, and it's > silly for so many sites to be squashing exceptionals out of the fbatch, > merely to suit an inadequacy in folios_put_refs(). > > But remove exceptionals on leaving truncate_folio_batch_exceptionals(), > one of whose callers then passes the fbatch on to others less tolerant. > > No longer essential to this series, since 7.2 commit 9669b87065a6 > ("mm/lruvec: preemptively free dead folios during lru_add drain") > allowed folios_put_refs() to skip NULLs; but still an improvement. > > Signed-off-by: Hugh Dickins > --- > include/linux/folio_batch.h | 5 +---- > mm/folio.c | 25 ++++--------------------- > mm/shmem.c | 2 -- > mm/truncate.c | 16 ++++++++++------ > 4 files changed, 15 insertions(+), 33 deletions(-) > > diff --git a/include/linux/folio_batch.h b/include/linux/folio_batch.h > index b45946adc50b..e1cc8ae023f1 100644 > --- a/include/linux/folio_batch.h > +++ b/include/linux/folio_batch.h > @@ -22,8 +22,7 @@ struct folio; > * The folio_batch is used to amortise the cost of retrieving and > * operating on a set of folios. The order of folios in the batch may be > * significant (eg delete_from_page_cache_batch()). Some users of the > - * folio_batch store "exceptional" entries in it which can be removed > - * by calling folio_batch_remove_exceptionals(). > + * folio_batch store "exceptional" (xa_is_value) entries in it too. > */ > struct folio_batch { > unsigned char nr; > @@ -100,6 +99,4 @@ static inline void folio_batch_release(struct folio_batch *fbatch) > if (folio_batch_count(fbatch)) > __folio_batch_release(fbatch); > } > - > -void folio_batch_remove_exceptionals(struct folio_batch *fbatch); > #endif /* _LINUX_FOLIO_BATCH_H */ > diff --git a/mm/folio.c b/mm/folio.c > index 62b96c9ce19e..b2bce6b77498 100644 > --- a/mm/folio.c > +++ b/mm/folio.c > @@ -983,6 +983,10 @@ void folios_put_refs(struct folio_batch *folios, unsigned int *refs) > if (!folio) > continue; > > + /* Skip any "exceptional" (workingset or shmem swap) entry. */ > + if (xa_is_value(folio)) > + continue; > + > if (is_huge_zero_folio(folio)) > continue; > > @@ -1088,27 +1092,6 @@ void __folio_batch_release(struct folio_batch *fbatch) > } > EXPORT_SYMBOL(__folio_batch_release); > > -/** > - * folio_batch_remove_exceptionals() - Prune non-folios from a batch. > - * @fbatch: The batch to prune > - * > - * find_get_entries() fills a batch with both folios and shadow/swap/DAX > - * entries. This function prunes all the non-folio entries from @fbatch > - * without leaving holes, so that it can be passed on to folio-only batch > - * operations. > - */ > -void folio_batch_remove_exceptionals(struct folio_batch *fbatch) > -{ > - unsigned int i, j; > - > - for (i = 0, j = 0; i < folio_batch_count(fbatch); i++) { > - struct folio *folio = fbatch->folios[i]; > - if (!xa_is_value(folio)) > - fbatch->folios[j++] = folio; > - } > - fbatch->nr = j; > -} > - > #ifdef CONFIG_MEMCG > static void lruvec_reparent_lru(struct lruvec *child_lruvec, > struct lruvec *parent_lruvec, > diff --git a/mm/shmem.c b/mm/shmem.c > index 89a1495e55f7..3911721e1e55 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -1156,7 +1156,6 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, uoff_t lend, > truncate_inode_folio(mapping, folio); > folio_unlock(folio); > } > - folio_batch_remove_exceptionals(&fbatch); > folio_batch_release(&fbatch); > cond_resched(); > } > @@ -1276,7 +1275,6 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, uoff_t lend, > } > folio_unlock(folio); > } > - folio_batch_remove_exceptionals(&fbatch); > folio_batch_release(&fbatch); > } > > diff --git a/mm/truncate.c b/mm/truncate.c > index b58ba940be47..4151f7a167e3 100644 > --- a/mm/truncate.c > +++ b/mm/truncate.c > @@ -53,7 +53,7 @@ static void clear_shadow_entries(struct address_space *mapping, > /* > * Unconditionally remove exceptional entries. Usually called from truncate > * path. Note that the folio_batch may be altered by this function by removing > - * exceptional entries similar to what folio_batch_remove_exceptionals() does. > + * exceptional entries. > * Please note that indices[] has entries in ascending order as guaranteed by > * either find_get_entries() or find_lock_entries(). > */ > @@ -95,7 +95,7 @@ static void truncate_folio_batch_exceptionals(struct address_space *mapping, > dax_delete_mapping_entry(mapping, indices[i]); > } > } > - goto out; > + goto squash; > } > > xas_set(&xas, indices[j]); > @@ -113,8 +113,14 @@ static void truncate_folio_batch_exceptionals(struct address_space *mapping, > if (mapping_shrinkable(mapping)) > inode_lru_list_add(mapping->host); > spin_unlock(&mapping->host->i_lock); > -out: > - folio_batch_remove_exceptionals(fbatch); > + > +squash: > + for (i = j + 1; i < nr; i++) { > + folio = fbatch->folios[i]; > + if (!xa_is_value(folio)) > + fbatch->folios[j++] = folio; > + } > + fbatch->nr = j; > } One caller of truncate_folio_batch_exceptionals() just calls folio_batch_release(). I was wondering whether that one could just stop calling truncate_folio_batch_exceptionals(). But truncate_folio_batch_exceptionals() does too many other things I don't quite understand. I guess one could move the loop into the only remaining caller that does not call folio_batch_release() afterwards. But that changes the whole purpose of the function and the name would no longer match. Which brings me back to my point that truncate_folio_batch_exceptionals() does a lot of things besides folio_batch_remove_exceptionals() that I don't understand :) So I'm sure there is room for future cleanups for somebody that actually understands what truncate_folio_batch_exceptionals() does besides ... removing exceptionals. Acked-by: David Hildenbrand (Arm) -- Cheers, David