| Message ID | 20191009222658.961-1-vgupta@synopsys.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | eldie generated code for folded p4d/pud | expand |
On Wed, Oct 09, 2019 at 03:26:55PM -0700, Vineet Gupta wrote: > Hi, > > This series elides extraneous generate code for folded p4d/pud. > This came up when trying to remove __ARCH_USE_5LEVEL_HACK from ARC port. > The code saving are not a while lot, but still worthwhile IMHO. > > bloat-o-meter2 vmlinux-A-baseline vmlinux-E-elide-p?d_clear_bad > add/remove: 0/2 grow/shrink: 0/1 up/down: 0/-146 (-146) > function old new delta > p4d_clear_bad 2 - -2 > pud_clear_bad 20 - -20 > free_pgd_range 546 422 -124 > Total: Before=4137148, After=4137002, chg -1.000000% > Works for me, thanks!
On Wed, Oct 09, 2019 at 10:26:55PM +0000, Vineet Gupta wrote: > Hi, > > This series elides extraneous generate code for folded p4d/pud. > This came up when trying to remove __ARCH_USE_5LEVEL_HACK from ARC port. > The code saving are not a while lot, but still worthwhile IMHO. Agreed. Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Hi Kirill, On 10/10/19 1:56 AM, Kirill A. Shutemov wrote: > On Wed, Oct 09, 2019 at 10:26:55PM +0000, Vineet Gupta wrote: >> >> This series elides extraneous generate code for folded p4d/pud. >> This came up when trying to remove __ARCH_USE_5LEVEL_HACK from ARC port. >> The code saving are not a while lot, but still worthwhile IMHO. > > Agreed. Thx. So given we are folding pmd too, it seemed we could do the following as well. +#ifndef __PAGETABLE_PMD_FOLDED void pmd_clear_bad(pmd_t *); +#else +#define pmd_clear_bad(pmd) do { } while (0) +#endif +#ifndef __PAGETABLE_PMD_FOLDED void pmd_clear_bad(pmd_t *pmd) { pmd_ERROR(*pmd); pmd_clear(pmd); } +#endif I stared at generated code and it seems a bit wrong. free_pgd_range() -> pgd_none_or_clear_bad() is no longer checking for unmapped pgd entries as pgd_none/pgd_bad are all stubs returning 0. This whole pmd folding is a bit confusing considering I only revisit it every few years :-) Abstraction wise, __PAGETABLE_PMD_FOLDED only has pgd, pte but even in this regime bunch of pmd macros are still valid pmd_set(pmdp, ptep) { *pmdp.pud.p4d.pgd = (unsigned long)ptep } Is there a better way to make a mental model of this code folding. In an ideal world pmd folded would have meant pmd_* routines just vanish - poof. So in that sense I like your implementation under #[45]LEVEL_HACK where the level simply vanishes by code like #define p4d_t pgd_t. Perhaps there is lot of historic baggage, proliferated into arch code so hard to untangle. Thx, -Vineet
On Thu, Oct 10, 2019 at 01:05:56PM -0700, Vineet Gupta wrote: > > Hi Kirill, > > On 10/10/19 1:56 AM, Kirill A. Shutemov wrote: > > On Wed, Oct 09, 2019 at 10:26:55PM +0000, Vineet Gupta wrote: > >> > >> This series elides extraneous generate code for folded p4d/pud. > >> This came up when trying to remove __ARCH_USE_5LEVEL_HACK from ARC port. > >> The code saving are not a while lot, but still worthwhile IMHO. > > > > Agreed. > > Thx. > > So given we are folding pmd too, it seemed we could do the following as well. > > +#ifndef __PAGETABLE_PMD_FOLDED > void pmd_clear_bad(pmd_t *); > +#else > +#define pmd_clear_bad(pmd) do { } while (0) > +#endif > > +#ifndef __PAGETABLE_PMD_FOLDED > void pmd_clear_bad(pmd_t *pmd) > { > pmd_ERROR(*pmd); > pmd_clear(pmd); > } > +#endif > > I stared at generated code and it seems a bit wrong. > free_pgd_range() -> pgd_none_or_clear_bad() is no longer checking for unmapped pgd > entries as pgd_none/pgd_bad are all stubs returning 0. > > This whole pmd folding is a bit confusing considering I only revisit it every few > years :-) Abstraction wise, __PAGETABLE_PMD_FOLDED only has pgd, pte but even in > this regime bunch of pmd macros are still valid > > pmd_set(pmdp, ptep) { > *pmdp.pud.p4d.pgd = (unsigned long)ptep > } > > Is there a better way to make a mental model of this code folding. I don't have any. PMD folding predates me and have never looked at it closely. Quick look brings more confusion than clarity. :P > In an ideal world pmd folded would have meant pmd_* routines just vanish - poof. > So in that sense I like your implementation under #[45]LEVEL_HACK where the level > simply vanishes by code like #define p4d_t pgd_t. Perhaps there is lot of historic > baggage, proliferated into arch code so hard to untangle. In ideal world all these pgd/p4d/pud/pmd/pte should die and we have something more flexible to begin with. I played with this before: https://lore.kernel.org/lkml/20180424154355.mfjgkf47kdp2by4e@black.fi.intel.com/
Hi, This series elides extraneous generate code for folded p4d/pud. This came up when trying to remove __ARCH_USE_5LEVEL_HACK from ARC port. The code saving are not a while lot, but still worthwhile IMHO. bloat-o-meter2 vmlinux-A-baseline vmlinux-E-elide-p?d_clear_bad add/remove: 0/2 grow/shrink: 0/1 up/down: 0/-146 (-146) function old new delta p4d_clear_bad 2 - -2 pud_clear_bad 20 - -20 free_pgd_range 546 422 -124 Total: Before=4137148, After=4137002, chg -1.000000% Thx, -Vineet Vineet Gupta (3): asm-generic/tlb: stub out pud_free_tlb() if __PAGETABLE_PUD_FOLDED ... asm-generic/tlb: stub out p4d_free_tlb() if __PAGETABLE_P4D_FOLDED ... asm-generic/mm: stub out p{4,d}d_clear_bad() if __PAGETABLE_P{4,u}D_FOLDED include/asm-generic/4level-fixup.h | 2 -- include/asm-generic/5level-fixup.h | 2 -- include/asm-generic/pgtable.h | 11 +++++++++++ include/asm-generic/tlb.h | 8 ++++++-- mm/pgtable-generic.c | 4 ++++ 5 files changed, 21 insertions(+), 6 deletions(-)