Vlastimil Babka 8ea1d2a198 mm, frontswap: convert frontswap_enabled to static key ... I have noticed that frontswap.h first declares "frontswap_enabled" as extern bool variable, and then overrides it with "#define frontswap_enabled (1)" for CONFIG_FRONTSWAP=Y or (0) when disabled. The bool variable isn't actually instantiated anywhere. This all looks like an unfinished attempt to make frontswap_enabled reflect whether a backend is instantiated. But in the current state, all frontswap hooks call unconditionally into frontswap.c just to check if frontswap_ops is non-NULL. This should at least be checked inline, but we can further eliminate the overhead when CONFIG_FRONTSWAP is enabled and no backend registered, using a static key that is initially disabled, and gets enabled only upon first backend registration. Thus, checks for "frontswap_enabled" are replaced with "frontswap_enabled()" wrapping the static key check. There are two exceptions: - xen's selfballoon_process() was testing frontswap_enabled in code guarded by #ifdef CONFIG_FRONTSWAP, which was effectively always true when reachable. The patch just removes this check. Using frontswap_enabled() does not sound correct here, as this can be true even without xen's own backend being registered. - in SYSCALL_DEFINE2(swapon), change the check to IS_ENABLED(CONFIG_FRONTSWAP) as it seems the bitmap allocation cannot currently be postponed until a backend is registered. This means that frontswap will still have some memory overhead by being configured, but without a backend. After the patch, we can expect that some functions in frontswap.c are called only when frontswap_ops is non-NULL. Change the checks there to VM_BUG_ONs. While at it, convert other BUG_ONs to VM_BUG_ONs as frontswap has been stable for some time. [akpm@linux-foundation.org: coding-style fixes] Link: http://lkml.kernel.org/r/1463152235-9717-1-git-send-email-vbabka@suse.cz Signed-off-by: Vlastimil Babka <vbabka@suse.cz> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com> Cc: David Vrabel <david.vrabel@citrix.com> Cc: Juergen Gross <jgross@suse.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>		2016-07-26 16:19:19 -07:00
..
events	xen/events: Don't move disabled irqs	2016-05-24 12:58:54 +01:00
xen-pciback	xen-pciback: return proper values during BAR sizing	2016-06-24 10:53:03 +01:00
xenbus	xenbus: simplify xenbus_dev_request_and_reply()	2016-07-08 11:50:29 +01:00
xenfs
acpi.c
balloon.c	xen/balloon: Fix declared-but-not-defined warning	2016-06-23 11:36:15 +01:00
biomerge.c
cpu_hotplug.c
dbgp.c
efi.c	efi: Remove unnecessary (and buggy) .memmap initialization from the Xen EFI driver	2016-04-29 11:06:15 +02:00
evtchn.c	xen/evtchn: fix ring resize when binding new events	2016-05-04 16:37:01 +01:00
fallback.c
features.c
gntalloc.c
gntdev.c	xen/gntdev: reduce copy batch size to 16	2016-05-24 12:58:17 +01:00
grant-table.c
Kconfig
Makefile	Xen: don't warn about 2-byte wchar_t in efi	2016-05-24 12:58:18 +01:00
manage.c
mcelog.c
pci.c
pcpu.c
platform-pci.c
preempt.c
privcmd.c
privcmd.h
swiotlb-xen.c
sys-hypervisor.c
time.c
tmem.c
xen-acpi-cpuhotplug.c
xen-acpi-memhotplug.c
xen-acpi-pad.c
xen-acpi-processor.c	xen/acpi: allow xen-acpi-processor driver to load on Xen 4.7	2016-07-08 14:53:13 +01:00
xen-balloon.c
xen-scsiback.c	target: make close_session optional	2016-05-10 01:19:26 -07:00
xen-selfballoon.c	mm, frontswap: convert frontswap_enabled to static key	2016-07-26 16:19:19 -07:00
xen-stub.c
xlate_mmu.c