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Wong" To: "Pankaj Raghav (Samsung)" Cc: linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, mcgrof@kernel.org, gost.dev@samsung.com, akpm@linux-foundation.org, kbusch@kernel.org, chandan.babu@oracle.com, p.raghav@samsung.com, linux-kernel@vger.kernel.org, hare@suse.de, willy@infradead.org, linux-mm@kvack.org, david@fromorbit.com Subject: Re: [RFC v2 01/14] fs: Allow fine-grained control of folio sizes Message-ID: <20240213163431.GS6184@frogsfrogsfrogs> References: <20240213093713.1753368-1-kernel@pankajraghav.com> <20240213093713.1753368-2-kernel@pankajraghav.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240213093713.1753368-2-kernel@pankajraghav.com> X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: C6432120031 X-Stat-Signature: mk9m73xjbzwdnhgtda6yoefu3ryaafjn X-HE-Tag: 1707842076-746459 X-HE-Meta: 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 pRmNI/4m Rzj5aZ0YDzvpCrgoUyL60bsf6ioByDhadr/7dCJhL4StatCFATBDDfrlYTuwKpQE5LN6Y1WgnfdfNxDyNSLiDbIsDOrADJhbGFQE9XBmKi1tde21BlSISVoxMKbEvf6PcXG5CdInRxE3xFgu8jk4taHZQpHPUptCDwj0A/XD4tUJS9HO6LLFJrzfzFf5xpJZDwR+MBKLX8FPk8dd/RYPHaYlkwz/OZCFs31o3NwnoN0M/pHkOLGNHPnfyq9y4g6LUKA5FJHdXM/fxV7gMr9ayZBf7iOUQLrO8EtNRu12TI/ewH4ueC8Ny5Awy71C8YmuJJQCeOt55jGvkTlE= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Feb 13, 2024 at 10:37:00AM +0100, Pankaj Raghav (Samsung) wrote: > From: "Matthew Wilcox (Oracle)" > > Some filesystems want to be able to limit the maximum size of folios, > and some want to be able to ensure that folios are at least a certain > size. Add mapping_set_folio_orders() to allow this level of control. > The max folio order parameter is ignored and it is always set to > MAX_PAGECACHE_ORDER. Why? If MAX_PAGECACHE_ORDER is 8 and I instead pass in max==3, I'm going to be surprised by my constraint being ignored. Maybe I said that because I'm not prepared to handle an order-7 folio; or some customer will have some weird desire to twist this knob to make their workflow faster. --D > Signed-off-by: Matthew Wilcox (Oracle) > Signed-off-by: Pankaj Raghav > Signed-off-by: Luis Chamberlain > --- > include/linux/pagemap.h | 92 ++++++++++++++++++++++++++++++++--------- > 1 file changed, 73 insertions(+), 19 deletions(-) > > diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h > index 2df35e65557d..5618f762187b 100644 > --- a/include/linux/pagemap.h > +++ b/include/linux/pagemap.h > @@ -202,13 +202,18 @@ enum mapping_flags { > AS_EXITING = 4, /* final truncate in progress */ > /* writeback related tags are not used */ > AS_NO_WRITEBACK_TAGS = 5, > - AS_LARGE_FOLIO_SUPPORT = 6, > - AS_RELEASE_ALWAYS, /* Call ->release_folio(), even if no private data */ > - AS_STABLE_WRITES, /* must wait for writeback before modifying > + AS_RELEASE_ALWAYS = 6, /* Call ->release_folio(), even if no private data */ > + AS_STABLE_WRITES = 7, /* must wait for writeback before modifying > folio contents */ > - AS_UNMOVABLE, /* The mapping cannot be moved, ever */ > + AS_FOLIO_ORDER_MIN = 8, > + AS_FOLIO_ORDER_MAX = 13, /* Bit 8-17 are used for FOLIO_ORDER */ > + AS_UNMOVABLE = 18, /* The mapping cannot be moved, ever */ > }; > > +#define AS_FOLIO_ORDER_MIN_MASK 0x00001f00 > +#define AS_FOLIO_ORDER_MAX_MASK 0x0003e000 > +#define AS_FOLIO_ORDER_MASK (AS_FOLIO_ORDER_MIN_MASK | AS_FOLIO_ORDER_MAX_MASK) > + > /** > * mapping_set_error - record a writeback error in the address_space > * @mapping: the mapping in which an error should be set > @@ -344,6 +349,53 @@ static inline void mapping_set_gfp_mask(struct address_space *m, gfp_t mask) > m->gfp_mask = mask; > } > > +/* > + * There are some parts of the kernel which assume that PMD entries > + * are exactly HPAGE_PMD_ORDER. Those should be fixed, but until then, > + * limit the maximum allocation order to PMD size. I'm not aware of any > + * assumptions about maximum order if THP are disabled, but 8 seems like > + * a good order (that's 1MB if you're using 4kB pages) > + */ > +#ifdef CONFIG_TRANSPARENT_HUGEPAGE > +#define MAX_PAGECACHE_ORDER HPAGE_PMD_ORDER > +#else > +#define MAX_PAGECACHE_ORDER 8 > +#endif > + > +/* > + * mapping_set_folio_orders() - Set the range of folio sizes supported. > + * @mapping: The file. > + * @min: Minimum folio order (between 0-MAX_PAGECACHE_ORDER inclusive). > + * @max: Maximum folio order (between 0-MAX_PAGECACHE_ORDER inclusive). > + * > + * The filesystem should call this function in its inode constructor to > + * indicate which sizes of folio the VFS can use to cache the contents > + * of the file. This should only be used if the filesystem needs special > + * handling of folio sizes (ie there is something the core cannot know). > + * Do not tune it based on, eg, i_size. > + * > + * Context: This should not be called while the inode is active as it > + * is non-atomic. > + */ > +static inline void mapping_set_folio_orders(struct address_space *mapping, > + unsigned int min, unsigned int max) > +{ > + if (min == 1) > + min = 2; > + if (max < min) > + max = min; > + if (max > MAX_PAGECACHE_ORDER) > + max = MAX_PAGECACHE_ORDER; > + > + /* > + * XXX: max is ignored as only minimum folio order is supported > + * currently. > + */ > + mapping->flags = (mapping->flags & ~AS_FOLIO_ORDER_MASK) | > + (min << AS_FOLIO_ORDER_MIN) | > + (MAX_PAGECACHE_ORDER << AS_FOLIO_ORDER_MAX); > +} > + > /** > * mapping_set_large_folios() - Indicate the file supports large folios. > * @mapping: The file. > @@ -357,7 +409,22 @@ static inline void mapping_set_gfp_mask(struct address_space *m, gfp_t mask) > */ > static inline void mapping_set_large_folios(struct address_space *mapping) > { > - __set_bit(AS_LARGE_FOLIO_SUPPORT, &mapping->flags); > + mapping_set_folio_orders(mapping, 0, MAX_PAGECACHE_ORDER); > +} > + > +static inline unsigned int mapping_max_folio_order(struct address_space *mapping) > +{ > + return (mapping->flags & AS_FOLIO_ORDER_MAX_MASK) >> AS_FOLIO_ORDER_MAX; > +} > + > +static inline unsigned int mapping_min_folio_order(struct address_space *mapping) > +{ > + return (mapping->flags & AS_FOLIO_ORDER_MIN_MASK) >> AS_FOLIO_ORDER_MIN; > +} > + > +static inline unsigned int mapping_min_folio_nrpages(struct address_space *mapping) > +{ > + return 1U << mapping_min_folio_order(mapping); > } > > /* > @@ -367,7 +434,7 @@ static inline void mapping_set_large_folios(struct address_space *mapping) > static inline bool mapping_large_folio_support(struct address_space *mapping) > { > return IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && > - test_bit(AS_LARGE_FOLIO_SUPPORT, &mapping->flags); > + (mapping_max_folio_order(mapping) > 0); > } > > static inline int filemap_nr_thps(struct address_space *mapping) > @@ -528,19 +595,6 @@ static inline void *detach_page_private(struct page *page) > return folio_detach_private(page_folio(page)); > } > > -/* > - * There are some parts of the kernel which assume that PMD entries > - * are exactly HPAGE_PMD_ORDER. Those should be fixed, but until then, > - * limit the maximum allocation order to PMD size. I'm not aware of any > - * assumptions about maximum order if THP are disabled, but 8 seems like > - * a good order (that's 1MB if you're using 4kB pages) > - */ > -#ifdef CONFIG_TRANSPARENT_HUGEPAGE > -#define MAX_PAGECACHE_ORDER HPAGE_PMD_ORDER > -#else > -#define MAX_PAGECACHE_ORDER 8 > -#endif > - > #ifdef CONFIG_NUMA > struct folio *filemap_alloc_folio(gfp_t gfp, unsigned int order); > #else > -- > 2.43.0 > >