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filemap: Allow __filemap_get_folio to allocate large folios

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Allow callers of __filemap_get_folio() to specify a preferred folio
order in the FGP flags.  This is only honoured in the FGP_CREATE path;
if there is already a folio in the page cache that covers the index,
we will return it, no matter what its order is.  No create-around is
attempted; we will only create folios which start at the specified index.
Unmodified callers will continue to allocate order 0 folios.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
This commit is contained in:
Matthew Wilcox (Oracle) 2023-05-19 16:10:37 -04:00
parent ffc143db63
commit 4f66170119
3 changed files with 67 additions and 26 deletions
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34
include/linux/pagemap.h
View File

@ -470,6 +470,19 @@ 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
@ -535,9 +548,30 @@ typedef unsigned int __bitwise fgf_t;
#define FGP_NOWAIT ((__force fgf_t)0x00000020)
#define FGP_FOR_MMAP ((__force fgf_t)0x00000040)
#define FGP_STABLE ((__force fgf_t)0x00000080)
#define FGF_GET_ORDER(fgf) (((__force unsigned)fgf) >> 26) /* top 6 bits */
#define FGP_WRITEBEGIN (FGP_LOCK | FGP_WRITE | FGP_CREAT | FGP_STABLE)
/**
* fgf_set_order - Encode a length in the fgf_t flags.
* @size: The suggested size of the folio to create.
*
* The caller of __filemap_get_folio() can use this to suggest a preferred
* size for the folio that is created. If there is already a folio at
* the index, it will be returned, no matter what its size. If a folio
* is freshly created, it may be of a different size than requested
* due to alignment constraints, memory pressure, or the presence of
* other folios at nearby indices.
*/
static inline fgf_t fgf_set_order(size_t size)
{
unsigned int shift = ilog2(size);
if (shift <= PAGE_SHIFT)
return 0;
return (__force fgf_t)((shift - PAGE_SHIFT) << 26);
}
void *filemap_get_entry(struct address_space *mapping, pgoff_t index);
struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
fgf_t fgp_flags, gfp_t gfp);

46
mm/filemap.c
View File

@ -1905,7 +1905,9 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
folio_wait_stable(folio);
no_page:
if (!folio && (fgp_flags & FGP_CREAT)) {
unsigned order = FGF_GET_ORDER(fgp_flags);
int err;
if ((fgp_flags & FGP_WRITE) && mapping_can_writeback(mapping))
gfp |= __GFP_WRITE;
if (fgp_flags & FGP_NOFS)
@ -1914,26 +1916,44 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
gfp &= ~GFP_KERNEL;
gfp |= GFP_NOWAIT | __GFP_NOWARN;
}
folio = filemap_alloc_folio(gfp, 0);
if (!folio)
return ERR_PTR(-ENOMEM);
if (WARN_ON_ONCE(!(fgp_flags & (FGP_LOCK | FGP_FOR_MMAP))))
fgp_flags |= FGP_LOCK;
/* Init accessed so avoid atomic mark_page_accessed later */
if (fgp_flags & FGP_ACCESSED)
__folio_set_referenced(folio);
if (!mapping_large_folio_support(mapping))
order = 0;
if (order > MAX_PAGECACHE_ORDER)
order = MAX_PAGECACHE_ORDER;
/* If we're not aligned, allocate a smaller folio */
if (index & ((1UL << order) - 1))
order = __ffs(index);
err = filemap_add_folio(mapping, folio, index, gfp);
if (unlikely(err)) {
do {
gfp_t alloc_gfp = gfp;
err = -ENOMEM;
if (order == 1)
order = 0;
if (order > 0)
alloc_gfp |= __GFP_NORETRY | __GFP_NOWARN;
folio = filemap_alloc_folio(alloc_gfp, order);
if (!folio)
continue;
/* Init accessed so avoid atomic mark_page_accessed later */
if (fgp_flags & FGP_ACCESSED)
__folio_set_referenced(folio);
err = filemap_add_folio(mapping, folio, index, gfp);
if (!err)
break;
folio_put(folio);
folio = NULL;
if (err == -EEXIST)
goto repeat;
}
} while (order-- > 0);
if (err == -EEXIST)
goto repeat;
if (err)
return ERR_PTR(err);
/*
* filemap_add_folio locks the page, and for mmap
* we expect an unlocked page.

13
mm/readahead.c
View File

@ -461,19 +461,6 @@ static int try_context_readahead(struct address_space *mapping,
return 1;
}
/*
* 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
static inline int ra_alloc_folio(struct readahead_control *ractl, pgoff_t index,
pgoff_t mark, unsigned int order, gfp_t gfp)
{