On Fri, Nov 25, 2016 at 4:59 PM, Dan Streetman <ddstr...@ieee.org> wrote: > On Tue, Nov 15, 2016 at 11:00 AM, Vitaly Wool <vitalyw...@gmail.com> wrote: >> Currently the whole kernel build will be stopped if the size of >> struct z3fold_header is greater than the size of one chunk, which >> is 64 bytes by default. This may stand in the way of automated >> test/debug builds so let's remove that and just fail the z3fold >> initialization in such case instead. >> >> Signed-off-by: Vitaly Wool <vitalyw...@gmail.com> >> --- >> mm/z3fold.c | 11 ++++++++--- >> 1 file changed, 8 insertions(+), 3 deletions(-) >> >> diff --git a/mm/z3fold.c b/mm/z3fold.c >> index 7ad70fa..ffd9353 100644 >> --- a/mm/z3fold.c >> +++ b/mm/z3fold.c >> @@ -870,10 +870,15 @@ MODULE_ALIAS("zpool-z3fold"); >> >> static int __init init_z3fold(void) >> { >> - /* Make sure the z3fold header will fit in one chunk */ >> - BUILD_BUG_ON(sizeof(struct z3fold_header) > ZHDR_SIZE_ALIGNED); > > Nak. this is the wrong way to handle this. The build bug is there to > indicate to you that your patch makes the header too large, not as a > runtime check to disable everything.
Okay, let's agree to drop it. > The right way to handle it is to change the hardcoded assumption that > the header fits into a single chunk; e.g.: > > #define ZHDR_SIZE_ALIGNED round_up(sizeof(struct z3fold_header), CHUNK_SIZE) > #define ZHDR_CHUNKS (ZHDR_SIZE_ALIGNED >> CHUNK_SHIFT) > > then use ZHDR_CHUNKS in all places where it's currently assumed the > header is 1 chunk, e.g. in num_free_chunks: > > if (zhdr->middle_chunks != 0) { > int nfree_before = zhdr->first_chunks ? > - 0 : zhdr->start_middle - 1; > + 0 : zhdr->start_middle - ZHDR_CHUNKS; > > after changing all needed places like that, the build bug isn't needed > anymore (unless we want to make sure the header isn't larger than some > arbitrary number N chunks) That sounds overly complicated to me. I would rather use bit_spin_lock as Arnd suggested. What would you say? ~vitaly