tmpfs: convert shmem_getpage_gfp to radix-swap
Convert shmem_getpage_gfp(), the engine-room of shmem, to expect page or swap entry returned from radix tree by find_lock_page(). Whereas the repetitive old method proceeded mainly under info->lock, dropping and repeating whenever one of the conditions needed was not met, now we can proceed without it, leaving shmem_add_to_page_cache() to check for a race. This way there is no need to preallocate a page, no need for an early radix_tree_preload(), no need for mem_cgroup_shmem_charge_fallback(). Move the error unwinding down to the bottom instead of repeating it throughout. ENOSPC handling is a little different from before: there is no longer any race between find_lock_page() and finding swap, but we can arrive at ENOSPC before calling shmem_recalc_inode(), which might occasionally discover freed space. Be stricter to check i_size before returning. info->lock is used for little but alloced, swapped, i_blocks updates. Move i_blocks updates out from under the max_blocks check, so even an unlimited size=0 mount can show accurate du. Signed-off-by: Hugh Dickins <hughd@google.com> Acked-by: Rik van Riel <riel@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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