On Wed, Jun 24, 2009 at 11:39:02AM -0500, Eric Sandeen wrote: > Eric Sandeen wrote: > > Theodore Tso wrote: > > >> I can see some things we can do to optimize stack usage; for example, > >> struct ext4_allocation_request is allocated on the stack, and the > >> structure was laid out without any regard to space wastage caused by > >> alignment requirements. That won't help on x86 at all, but it will > >> help substantially on x86_64 (since x86_64 requires that 8 byte > >> variables must be 8-byte aligned, where as x86_64 only requires 4 byte > >> alignment, even for unsigned long long's). But it's going have to be > >> a whole series of incremental improvements; I don't see any magic > >> bullet solution to our stack usage. > > > > XFS forces gcc to not inline any static function; it's extreme, but > > maybe it'd help here too. > > Giving a blanket noinline treatment to mballoc.c yields some significant > stack savings: So stupid question. I can see how using noinline reduces the static stack savings, but does it actually reduce the run-time stack usage? After all, if function ext4_mb_foo() call ext4_mb_bar(), using noinline is a great way for seeing which function is actually responsible for chewing up disk space, but if ext4_mb_foo() always calls ext4_mb_bar(), and ext4_mb_bar() is a static inline only called once by ext4_mb_foo() unconditionally, won't we ultimately end up using more disk space (since we also have to save registers and save the return address on the stack)? - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
