Also convert should_try_to_free_swap() to use a folio.  This removes a few
calls to compound_head().

Link: https://lkml.kernel.org/r/20220902194653.1739778-47-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Replace three calls to compound_head() with one.

Link: https://lkml.kernel.org/r/20220902194653.1739778-46-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Remove a few hidden calls to compound_head().

Link: https://lkml.kernel.org/r/20220902194653.1739778-45-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Saves a lot of calls to compound_head().

Link: https://lkml.kernel.org/r/20220902194653.1739778-44-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Removes many calls to compound_head().  Does not remove the assumption
that a folio may not be larger than a PMD.

Link: https://lkml.kernel.org/r/20220902194653.1739778-43-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Saves many calls to compound_head().

Link: https://lkml.kernel.org/r/20220902194653.1739778-42-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Removes many calls to compound_head().

Link: https://lkml.kernel.org/r/20220902194653.1739778-41-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Saves several calls to compound_head().

Link: https://lkml.kernel.org/r/20220902194653.1739778-40-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

All callers have now been converted to swap_cache_get_folio(), so we can
remove this wrapper.

Link: https://lkml.kernel.org/r/20220902194653.1739778-39-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Saves a folio->page->folio conversion.

Link: https://lkml.kernel.org/r/20220902194653.1739778-38-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Delay fetching the precise page from the folio until we're in unuse_pte().
Saves many calls to compound_head().

Link: https://lkml.kernel.org/r/20220902194653.1739778-37-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Saves five calls to compound_head().

Link: https://lkml.kernel.org/r/20220902194653.1739778-36-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Saves five calls to compound_head().

Link: https://lkml.kernel.org/r/20220902194653.1739778-35-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

With all callers removed, remove this wrapper function.  The flags are now
mysteriously called SGP, but I think we can live with that.

Link: https://lkml.kernel.org/r/20220902194653.1739778-34-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

shmem_getpage() is being replaced by shmem_get_folio() so use a folio
throughout this function.  Saves several calls to compound_head().

Link: https://lkml.kernel.org/r/20220902194653.1739778-33-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

shmem_getpage() is being removed, so call its replacement and find the
precise page ourselves.

Link: https://lkml.kernel.org/r/20220902194653.1739778-32-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Symlinks will never use a large folio, but using the folio API removes a
lot of unnecessary folio->page->folio conversions.

Link: https://lkml.kernel.org/r/20220902194653.1739778-31-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

While symlinks will always be < PAGE_SIZE, using the folio APIs gets rid
of unnecessary calls to compound_head().

Link: https://lkml.kernel.org/r/20220902194653.1739778-30-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Call shmem_get_folio() and use the folio APIs instead of the page APIs. 
Saves several calls to compound_head() and removes assumptions about the
size of a large folio.

Link: https://lkml.kernel.org/r/20220902194653.1739778-29-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Use a folio throughout, saving five calls to compound_head().

Link: https://lkml.kernel.org/r/20220902194653.1739778-28-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Use a folio throughout this function, saving a couple of calls to
compound_head().

Link: https://lkml.kernel.org/r/20220902194653.1739778-27-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Get rid of an unnecessary folio->page->folio conversion.

Link: https://lkml.kernel.org/r/20220902194653.1739778-26-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

With no remaining callers of shmem_getpage_gfp(), add shmem_get_folio()
and reimplement shmem_getpage() as a call to shmem_get_folio().

Link: https://lkml.kernel.org/r/20220902194653.1739778-25-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Saves a couple of calls to compound_head().

Link: https://lkml.kernel.org/r/20220902194653.1739778-24-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

No particular advantage for this function, but necessary to remove
shmem_getpage_gfp().

[hughd@google.com: fix crash]
  Link: https://lkml.kernel.org/r/7693a84-bdc2-27b5-2695-d0fe8566571f@google.com
Link: https://lkml.kernel.org/r/20220902194653.1739778-23-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Add a shmem_getpage_gfp() wrapper for compatibility with current users.

Link: https://lkml.kernel.org/r/20220902194653.1739778-22-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Convert shmem_swapin() to return a folio and use swap_cache_get_folio(),
removing all uses of struct page in this function.

Link: https://lkml.kernel.org/r/20220902194653.1739778-21-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Convert lookup_swap_cache() into swap_cache_get_folio() and add a
lookup_swap_cache() wrapper around it.

[akpm@linux-foundation.org: add CONFIG_SWAP=n stub for swap_cache_get_folio()]
Link: https://lkml.kernel.org/r/20220902194653.1739778-20-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

The caller has a folio, so convert the calling convention and rename the
function.

Link: https://lkml.kernel.org/r/20220902194653.1739778-19-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Assert that this is a single-page folio as there are several assumptions
in here that it's exactly PAGE_SIZE bytes large.  Saves several calls to
compound_head() and removes the last caller of shmem_alloc_page().

Link: https://lkml.kernel.org/r/20220902194653.1739778-18-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

All callers now have a folio, so pass it in here and remove an unnecessary
call to page_folio().

Link: https://lkml.kernel.org/r/20220902194653.1739778-17-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

The 'swapcache' variable is used to track whether the page is from the
swapcache or not.  It can do this equally well by being the folio of the
page rather than the page itself, and this saves a number of calls to
compound_head().

Link: https://lkml.kernel.org/r/20220902194653.1739778-16-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Removes quite a lot of calls to compound_head().

Link: https://lkml.kernel.org/r/20220902194653.1739778-15-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

With all callers now using a folio, we can convert this function.

Link: https://lkml.kernel.org/r/20220902194653.1739778-14-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

With all callers using folios, we can convert add_to_swap_cache() to take
a folio and use it throughout.

Link: https://lkml.kernel.org/r/20220902194653.1739778-13-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Remove a few hidden (and one visible) calls to compound_head().

Link: https://lkml.kernel.org/r/20220902194653.1739778-12-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Add kernel-doc for folio_free_swap() and make it return bool.  Add a
try_to_free_swap() compatibility wrapper.

Link: https://lkml.kernel.org/r/20220902194653.1739778-11-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

By restructuring folio_swapped(), it can use swap_swapcount() instead of
page_swapcount().  It's even a little more efficient.

Link: https://lkml.kernel.org/r/20220902194653.1739778-10-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Introduce folio_set_swap_entry() to abstract how both folio->private and
swp_entry_t work.  Use swap_address_space() directly instead of
indirecting through folio_mapping().  Include an assertion that the old
folio is not large as we only allocate a single-page folio to replace it. 
Use folio_put_refs() instead of calling folio_put() twice.

Link: https://lkml.kernel.org/r/20220902194653.1739778-9-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Remove the assertion that the page is not Compound as this function now
handles large folios correctly.

Link: https://lkml.kernel.org/r/20220902194653.1739778-8-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>