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mm: add FGP_DONTCACHE folio creation flag

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Callers can pass this in for uncached folio creation, in which case if a
folio is newly created it gets marked as uncached.  If a folio exists for
this index and lookup succeeds, then it will not get marked as uncached. 
If an !uncached lookup finds a cached folio, clear the flag.  For that
case, there are competeting uncached and cached users of the folio, and it
should not get pruned.

Link: https://lkml.kernel.org/r/20241220154831.1086649-13-axboe@kernel.dk
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Cc: Brian Foster <bfoster@redhat.com>
Cc: Chris Mason <clm@meta.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Jens Axboe 2024-12-20 08:47:50 -07:00 committed by Andrew Morton
parent b76a5232eb
commit 8fbed73d40
2 changed files with 7 additions and 0 deletions
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2
include/linux/pagemap.h
View File

@ -721,6 +721,7 @@ pgoff_t page_cache_prev_miss(struct address_space *mapping,
* * %FGP_NOFS - __GFP_FS will get cleared in gfp.
* * %FGP_NOWAIT - Don't block on the folio lock.
* * %FGP_STABLE - Wait for the folio to be stable (finished writeback)
* * %FGP_DONTCACHE - Uncached buffered IO
* * %FGP_WRITEBEGIN - The flags to use in a filesystem write_begin()
* implementation.
*/
@ -734,6 +735,7 @@ 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 FGP_DONTCACHE ((__force fgf_t)0x00000100)
#define FGF_GET_ORDER(fgf) (((__force unsigned)fgf) >> 26) /* top 6 bits */
#define FGP_WRITEBEGIN (FGP_LOCK | FGP_WRITE | FGP_CREAT | FGP_STABLE)

5
mm/filemap.c
View File

@ -1973,6 +1973,8 @@ no_page:
/* Init accessed so avoid atomic mark_page_accessed later */
if (fgp_flags & FGP_ACCESSED)
__folio_set_referenced(folio);
if (fgp_flags & FGP_DONTCACHE)
__folio_set_dropbehind(folio);
err = filemap_add_folio(mapping, folio, index, gfp);
if (!err)
@ -1995,6 +1997,9 @@ no_page:
if (!folio)
return ERR_PTR(-ENOENT);
/* not an uncached lookup, clear uncached if set */
if (folio_test_dropbehind(folio) && !(fgp_flags & FGP_DONTCACHE))
folio_clear_dropbehind(folio);
return folio;
}
EXPORT_SYMBOL(__filemap_get_folio);