On Sun 25-02-24 01:12:46, Suren Baghdasaryan wrote: > On Sat, Feb 24, 2024 at 7:03 AM Christophe JAILLET > <christophe.jaillet@xxxxxxxxxx> wrote: > > > > Le 24/02/2024 à 02:58, Suren Baghdasaryan a écrit : > > > Introduce GFP bits enumeration to let compiler track the number of used > > > bits (which depends on the config options) instead of hardcoding them. > > > That simplifies __GFP_BITS_SHIFT calculation. > > > > > > Suggested-by: Petr Tesařík <petr@xxxxxxxxxxx> > > > Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx> > > > Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> > > > Reviewed-by: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx> > > > Acked-by: Michal Hocko <mhocko@xxxxxxxx> > > > --- > > > Changes from v4 [1]: > > > - Split from the series [2] as a stand-alone patch, per Michal Hocko > > > - Added Reviewed-by, per Pasha Tatashin > > > - Added Acked-by, per Michal Hocko > > > > > > [1] https://lore.kernel.org/all/20240221194052.927623-7-surenb@xxxxxxxxxx/ > > > [2] https://lore.kernel.org/all/20240221194052.927623-1-surenb@xxxxxxxxxx/ > > > > > > include/linux/gfp_types.h | 90 +++++++++++++++++++++++++++------------ > > > 1 file changed, 62 insertions(+), 28 deletions(-) > > > > > > diff --git a/include/linux/gfp_types.h b/include/linux/gfp_types.h > > > index 1b6053da8754..868c8fb1bbc1 100644 > > > --- a/include/linux/gfp_types.h > > > +++ b/include/linux/gfp_types.h > > > @@ -21,44 +21,78 @@ typedef unsigned int __bitwise gfp_t; > > > * include/trace/events/mmflags.h and tools/perf/builtin-kmem.c > > > */ > > > > > > +enum { > > > + ___GFP_DMA_BIT, > > > + ___GFP_HIGHMEM_BIT, > > > + ___GFP_DMA32_BIT, > > > + ___GFP_MOVABLE_BIT, > > > + ___GFP_RECLAIMABLE_BIT, > > > + ___GFP_HIGH_BIT, > > > + ___GFP_IO_BIT, > > > + ___GFP_FS_BIT, > > > + ___GFP_ZERO_BIT, > > > + ___GFP_UNUSED_BIT, /* 0x200u unused */ > > > > Hi, > > > > what is the need to have this ___GFP_UNUSED_BIT now? > > Hi! > We can remove it but then all values will shift. That should be safe > to do now but I prefer one patch to do only one thing. We can add a > separate patch to do further cleanup of unused values. Agreed! > > > + ___GFP_DIRECT_RECLAIM_BIT, > > > + ___GFP_KSWAPD_RECLAIM_BIT, > > > + ___GFP_WRITE_BIT, > > > + ___GFP_NOWARN_BIT, > > > + ___GFP_RETRY_MAYFAIL_BIT, > > > + ___GFP_NOFAIL_BIT, > > > + ___GFP_NORETRY_BIT, > > > + ___GFP_MEMALLOC_BIT, > > > + ___GFP_COMP_BIT, > > > + ___GFP_NOMEMALLOC_BIT, > > > + ___GFP_HARDWALL_BIT, > > > + ___GFP_THISNODE_BIT, > > > + ___GFP_ACCOUNT_BIT, > > > + ___GFP_ZEROTAGS_BIT, > > > +#ifdef CONFIG_KASAN_HW_TAGS > > > + ___GFP_SKIP_ZERO_BIT, > > > + ___GFP_SKIP_KASAN_BIT, > > > +#endif > > > +#ifdef CONFIG_LOCKDEP > > > + ___GFP_NOLOCKDEP_BIT, > > > +#endif > > > + ___GFP_LAST_BIT > > > +}; > > > > Does it make sense to have something like: > > BUILD_BUG_ON(___GFP_LAST_BIT > BITS_PER_LONG, "blah"); > > I suppose that would not hurt, except gfp_t is unsigned int, not long. > Something like this would work I think: > > BUILD_BUG_ON_MSG(___GFP_LAST_BIT > BITS_PER_TYPE(gfp_t), "GFP bit overflow"); > > except I'm not sure where to put this check. One of the __init > functions in page_alloc.c would probably work but none seem to be > appropriate. mm_core_init() perhaps? Other ideas? Would that check add much? We currently cannot use the full width of the gfp_t because radix tree code needs to fit also its own tag into the same word (see radix_tree_init). If the radix tree constrain is lifted then we should add something like the above. -- Michal Hocko SUSE Labs
