RFC Fix linux/swap.h build wart

For some time, there has been a problem of linux/swap.h using page_cache_release and release_pages without declaring them by including linux/pagemap.h. pagemap.h isn't included because that breaks the sparc build.

The full details are in the next post, but the short story is that sparc's pgtable.h includes linux/swap.h, creating a mm.h -> mm.h recursion. The current tree breaks that recursion by removing the swap.h -> pagemap.h inclusion. This breaks builds on a regular basis (references also in the next post).

These patches propose to break the recursion instead by removing the linux/pagemap.h -> linux/highmem.h inclusion. I'd like to know whether there are any fundamental reasons that this include should be preserved.

The reason for choosing this include is that pagemap.h doesn't use anything exported by highmem.h. The downside is that a bunch of things now need to include highmem.h. These are mostly filesystems, plus a good amount of arch code and a few drivers. I would argue that if you use something from a header, you should include it, regardless of whether you already get the header indirectly, so this isn't too much of a downside as far as I'm concerned.

The one thing I'm uncertain about is whether pagemap.h and highmem.h have some basic relationship that implies that you can assume you get highmem when you include pagemap.

The two patches that follow do the following:
remove highmem.h from pagemap.h and add includes of highmem.h
to a number of files that now need them
include pagemap.h in swap.h

These are for comment only, not for mainline, so there's no S-o-b right yet.

At this point, I haven't confirmed that the following files, which use stuff from highmem.h but don't include it, still build:

	./arch/x86/kernel/crash_dump_64.c
	./arch/frv/mm/fault.c
	./arch/frv/mm/kmap.c
	./arch/h8300/mm/kmap.c
	./arch/ia64/kernel/crash_dump.c
	./arch/m68k/mm/kmap.c
	./arch/m68knommu/mm/kmap.c
	./arch/powerpc/kernel/crash_dump.c
	./arch/sh/kernel/crash_dump.c
	./arch/xtensa/mm/pgtable.c
	./drivers/block/ps3disk.c
	./drivers/infiniband/hw/ipath/ipath_verbs.h
	./drivers/mmc/host/at91_mci.c
	./drivers/mmc/host/mmci.h
	./drivers/mmc/host/mmc_spi.c
	./drivers/s390/block/xpram.c
	./drivers/s390/char/tape_34xx.c
	./drivers/kvm/paging_tmpl.h
	./fs/hfsplus/hfsplus_fs.h
	./include/asm-arm/cacheflush.h
	./include/asm-frv/pgtable.h
	./include/asm-x86/kexec_32.h
	./include/asm-x86/kexec_64.h
	./include/asm-x86/pgtable_32.h
	./include/asm-m68k/motorola_pgalloc.h
	./include/asm-m68k/sun3_pgalloc.h
	./include/asm-m68k/sun3_pgtable.h
	./include/asm-mips/cacheflush.h
	./include/asm-mips/page.h
	./include/asm-parisc/cacheflush.h
	./include/asm-powerpc/pgtable-ppc32.h
	./include/asm-ppc/pgtable.h
	./include/asm-s390/kexec.h
	./include/asm-sh/kexec.h
	./mm/migrate.c

				Jeff

Work email - jdike at linux dot intel dot com