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Message-ID: <cb644a36-67a7-4692-b002-413e70ac864a@arm.com>
Date: Thu, 4 Jul 2024 13:23:20 +0100
From: Ryan Roberts <ryan.roberts@....com>
To: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>, david@...morbit.com,
willy@...radead.org, chandan.babu@...cle.com, djwong@...nel.org,
brauner@...nel.org, akpm@...ux-foundation.org
Cc: linux-kernel@...r.kernel.org, yang@...amperecomputing.com,
linux-mm@...ck.org, john.g.garry@...cle.com, linux-fsdevel@...r.kernel.org,
hare@...e.de, p.raghav@...sung.com, mcgrof@...nel.org, gost.dev@...sung.com,
cl@...amperecomputing.com, linux-xfs@...r.kernel.org, hch@....de,
Zi Yan <zi.yan@...t.com>
Subject: Re: [PATCH v8 01/10] fs: Allow fine-grained control of folio sizes
Hi,
Here are some drive-by review comments as I'm evaluating whether these patches
can help me with what I'm trying to do at
https://lore.kernel.org/linux-mm/20240215154059.2863126-1-ryan.roberts@arm.com/...
On 25/06/2024 12:44, Pankaj Raghav (Samsung) wrote:
> From: "Matthew Wilcox (Oracle)" <willy@...radead.org>
>
> We need filesystems to be able to communicate acceptable folio sizes
> to the pagecache for a variety of uses (e.g. large block sizes).
> Support a range of folio sizes between order-0 and order-31.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> Co-developed-by: Pankaj Raghav <p.raghav@...sung.com>
> Signed-off-by: Pankaj Raghav <p.raghav@...sung.com>
> Reviewed-by: Hannes Reinecke <hare@...e.de>
> Reviewed-by: Darrick J. Wong <djwong@...nel.org>
> ---
> include/linux/pagemap.h | 86 ++++++++++++++++++++++++++++++++++-------
> mm/filemap.c | 6 +--
> mm/readahead.c | 4 +-
> 3 files changed, 77 insertions(+), 19 deletions(-)
>
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index 4b71d581091f..0c51154cdb57 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -204,14 +204,21 @@ 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,
nit: this removed enum is still referenced in a comment further down the file.
> - 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_INACCESSIBLE, /* Do not attempt direct R/W access to the mapping */
> + AS_UNMOVABLE = 8, /* The mapping cannot be moved, ever */
> + AS_INACCESSIBLE = 9, /* Do not attempt direct R/W access to the mapping */
> + /* Bits 16-25 are used for FOLIO_ORDER */
> + AS_FOLIO_ORDER_BITS = 5,
> + AS_FOLIO_ORDER_MIN = 16,
> + AS_FOLIO_ORDER_MAX = AS_FOLIO_ORDER_MIN + AS_FOLIO_ORDER_BITS,
nit: These 3 new enums seem a bit odd. It might be clearer if you just reserve
the bits for the fields here? AS_FOLIO_ORDER_BITS isn't actually a flags bit and
the MAX value is currently the start of the max field, not the end.
#define AS_FOLIO_ORDER_BITS 5
enum mapping_flags {
...
AS_FOLIO_ORDERS_FIRST = 16,
AS_FOLIO_ORDERS_LAST = AS_FOLIO_ORDERS_FIRST+(2*AS_FOLIO_ORDER_BITS)-1,
...
};
#define AS_FOLIO_ORDER_MIN_MASK \
GENMASK(AS_FOLIO_ORDERS_FIRST + AS_FOLIO_ORDER_BITS - 1, \
AS_FOLIO_ORDERS_FIRST)
#define AS_FOLIO_ORDER_MAX_MASK \
GENMASK(AS_FOLIO_ORDERS_LAST, \
AS_FOLIO_ORDERS_LAST - AS_FOLIO_ORDER_BITS + 1)
> };
>
> +#define AS_FOLIO_ORDER_MASK ((1u << AS_FOLIO_ORDER_BITS) - 1)
> +#define AS_FOLIO_ORDER_MIN_MASK (AS_FOLIO_ORDER_MASK << AS_FOLIO_ORDER_MIN)
> +#define AS_FOLIO_ORDER_MAX_MASK (AS_FOLIO_ORDER_MASK << AS_FOLIO_ORDER_MAX)
> +
> /**
> * mapping_set_error - record a writeback error in the address_space
> * @mapping: the mapping in which an error should be set
> @@ -360,9 +367,49 @@ static inline void mapping_set_gfp_mask(struct address_space *m, gfp_t mask)
> #define MAX_PAGECACHE_ORDER 8
> #endif
>
> +/*
> + * mapping_set_folio_order_range() - Set the orders supported by a file.
> + * @mapping: The address space of the file.
> + * @min: Minimum folio order (between 0-MAX_PAGECACHE_ORDER inclusive).
> + * @max: Maximum folio order (between @min-MAX_PAGECACHE_ORDER inclusive).
> + *
> + * The filesystem should call this function in its inode constructor to
> + * indicate which base size (min) and maximum size (max) 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_order_range(struct address_space *mapping,
> + unsigned int min,
> + unsigned int max)
> +{
> + if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE))
> + return;
> +
> + if (min > MAX_PAGECACHE_ORDER)
> + min = MAX_PAGECACHE_ORDER;
> + if (max > MAX_PAGECACHE_ORDER)
> + max = MAX_PAGECACHE_ORDER;
> + if (max < min)
> + max = min;
It seems strange to silently clamp these? Presumably for the bs>ps usecase,
whatever values are passed in are a hard requirement? So wouldn't want them to
be silently reduced. (Especially given the recent change to reduce the size of
MAX_PAGECACHE_ORDER to less then PMD size in some cases).
> +
> + mapping->flags = (mapping->flags & ~AS_FOLIO_ORDER_MASK) |
> + (min << AS_FOLIO_ORDER_MIN) | (max << AS_FOLIO_ORDER_MAX);
> +}
> +
> +static inline void mapping_set_folio_min_order(struct address_space *mapping,
> + unsigned int min)
> +{
> + mapping_set_folio_order_range(mapping, min, MAX_PAGECACHE_ORDER);
> +}
> +
> /**
> * mapping_set_large_folios() - Indicate the file supports large folios.
> - * @mapping: The file.
> + * @mapping: The address space of the file.
> *
> * The filesystem should call this function in its inode constructor to
> * indicate that the VFS can use large folios to cache the contents of
> @@ -373,7 +420,23 @@ 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_order_range(mapping, 0, MAX_PAGECACHE_ORDER);
> +}
> +
> +static inline
> +unsigned int mapping_max_folio_order(const struct address_space *mapping)
> +{
> + if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE))
> + return 0;
> + return (mapping->flags & AS_FOLIO_ORDER_MAX_MASK) >> AS_FOLIO_ORDER_MAX;
> +}
> +
> +static inline
> +unsigned int mapping_min_folio_order(const struct address_space *mapping)
> +{
> + if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE))
> + return 0;
> + return (mapping->flags & AS_FOLIO_ORDER_MIN_MASK) >> AS_FOLIO_ORDER_MIN;
> }
>
> /*
> @@ -386,16 +449,13 @@ static inline bool mapping_large_folio_support(struct address_space *mapping)
> VM_WARN_ONCE((unsigned long)mapping & PAGE_MAPPING_ANON,
> "Anonymous mapping always supports large folio");
>
> - return IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
> - test_bit(AS_LARGE_FOLIO_SUPPORT, &mapping->flags);
> + return mapping_max_folio_order(mapping) > 0;
> }
>
> /* Return the maximum folio size for this pagecache mapping, in bytes. */
> -static inline size_t mapping_max_folio_size(struct address_space *mapping)
> +static inline size_t mapping_max_folio_size(const struct address_space *mapping)
> {
> - if (mapping_large_folio_support(mapping))
> - return PAGE_SIZE << MAX_PAGECACHE_ORDER;
> - return PAGE_SIZE;
> + return PAGE_SIZE << mapping_max_folio_order(mapping);
> }
>
> static inline int filemap_nr_thps(struct address_space *mapping)
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 0b8c732bb643..d617c9afca51 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -1933,10 +1933,8 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
> if (WARN_ON_ONCE(!(fgp_flags & (FGP_LOCK | FGP_FOR_MMAP))))
> fgp_flags |= FGP_LOCK;
>
> - if (!mapping_large_folio_support(mapping))
> - order = 0;
> - if (order > MAX_PAGECACHE_ORDER)
> - order = MAX_PAGECACHE_ORDER;
> + if (order > mapping_max_folio_order(mapping))
> + order = mapping_max_folio_order(mapping);
> /* If we're not aligned, allocate a smaller folio */
> if (index & ((1UL << order) - 1))
> order = __ffs(index);
> diff --git a/mm/readahead.c b/mm/readahead.c
> index c1b23989d9ca..66058ae02f2e 100644
> --- a/mm/readahead.c
> +++ b/mm/readahead.c
> @@ -503,9 +503,9 @@ void page_cache_ra_order(struct readahead_control *ractl,
>
> limit = min(limit, index + ra->size - 1);
>
> - if (new_order < MAX_PAGECACHE_ORDER) {
> + if (new_order < mapping_max_folio_order(mapping)) {
> new_order += 2;
> - new_order = min_t(unsigned int, MAX_PAGECACHE_ORDER, new_order);
> + new_order = min(mapping_max_folio_order(mapping), new_order);
> new_order = min_t(unsigned int, new_order, ilog2(ra->size));
I wonder if its possible that ra->size could ever be less than
mapping_min_folio_order()? Do you need to handle that?
Thanks,
Ryan
> }
>
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