On Mon, Feb 04, 2013 at 03:05:15PM -0800, Neel Natu wrote: > Hi, > > I have a patch to dynamically calculate NKPT for amd64 kernels. This > should fix the various issues that people pointed out in the email > thread. > > Please review and let me know if there are any objections to committing this. > > Also, thanks to Alan (alc@) for reviewing and providing feedback on > the initial version of the patch. > > Patch (also available at > http://people.freebsd.org/~neel/patches/nkpt_diff.txt): > > Index: sys/amd64/include/pmap.h > =================================================================== > --- sys/amd64/include/pmap.h (revision 246277) > +++ sys/amd64/include/pmap.h (working copy) > @@ -113,13 +113,7 @@ > ((unsigned long)(l2) << PDRSHIFT) | \ > ((unsigned long)(l1) << PAGE_SHIFT)) > > -/* Initial number of kernel page tables. */ > -#ifndef NKPT > -#define NKPT 32 > -#endif > - > #define NKPML4E 1 /* number of kernel PML4 slots > */ > -#define NKPDPE howmany(NKPT, NPDEPG)/* number of kernel PDP > slots */ > > #define NUPML4E (NPML4EPG/2) /* number of userland PML4 > pages */ > #define NUPDPE (NUPML4E*NPDPEPG)/* number of userland PDP > pages */ > @@ -181,6 +175,7 @@ > #define PML4map ((pd_entry_t *)(addr_PML4map)) > #define PML4pml4e ((pd_entry_t *)(addr_PML4pml4e)) > > +extern int nkpt; /* Initial number of kernel page tables */ > extern u_int64_t KPDPphys; /* physical address of kernel level 3 */ > extern u_int64_t KPML4phys; /* physical address of kernel level 4 */ > > Index: sys/amd64/amd64/minidump_machdep.c > =================================================================== > --- sys/amd64/amd64/minidump_machdep.c (revision 246277) > +++ sys/amd64/amd64/minidump_machdep.c (working copy) > @@ -232,7 +232,7 @@ > /* Walk page table pages, set bits in vm_page_dump */ > pmapsize = 0; > pdp = (uint64_t *)PHYS_TO_DMAP(KPDPphys); > - for (va = VM_MIN_KERNEL_ADDRESS; va < MAX(KERNBASE + NKPT * NBPDR, > + for (va = VM_MIN_KERNEL_ADDRESS; va < MAX(KERNBASE + nkpt * NBPDR, > kernel_vm_end); ) { > /* > * We always write a page, even if it is zero. Each > @@ -364,7 +364,7 @@ > /* Dump kernel page directory pages */ > bzero(fakepd, sizeof(fakepd)); > pdp = (uint64_t *)PHYS_TO_DMAP(KPDPphys); > - for (va = VM_MIN_KERNEL_ADDRESS; va < MAX(KERNBASE + NKPT * NBPDR, > + for (va = VM_MIN_KERNEL_ADDRESS; va < MAX(KERNBASE + nkpt * NBPDR, > kernel_vm_end); va += NBPDP) { > i = (va >> PDPSHIFT) & ((1ul << NPDPEPGSHIFT) - 1); > > Index: sys/amd64/amd64/pmap.c > =================================================================== > --- sys/amd64/amd64/pmap.c (revision 246277) > +++ sys/amd64/amd64/pmap.c (working copy) > @@ -202,6 +202,10 @@ > vm_offset_t virtual_avail; /* VA of first avail page (after kernel bss) */ > vm_offset_t virtual_end; /* VA of last avail page (end of kernel AS) */ > > +int nkpt; > +SYSCTL_INT(_machdep, OID_AUTO, nkpt, CTLFLAG_RD, &nkpt, 0, > + "Number of kernel page table pages allocated on bootup"); > + > static int ndmpdp; > static vm_paddr_t dmaplimit; > vm_offset_t kernel_vm_end = VM_MIN_KERNEL_ADDRESS; > @@ -495,17 +499,42 @@ > > CTASSERT(powerof2(NDMPML4E)); > > +/* number of kernel PDP slots */ > +#define NKPDPE(ptpgs) howmany((ptpgs), NPDEPG) > + > static void > +nkpt_init(vm_paddr_t addr) > +{ > + int pt_pages; > + > +#ifdef NKPT > + pt_pages = NKPT; > +#else > + pt_pages = howmany(addr, 1 << PDRSHIFT); > + pt_pages += NKPDPE(pt_pages); > + > + /* > + * Add some slop beyond the bare minimum required for bootstrapping > + * the kernel. > + * > + * This is quite important when allocating KVA for kernel modules. > + * The modules are required to be linked in the negative 2GB of > + * the address space. If we run out of KVA in this region then > + * pmap_growkernel() will need to allocate page table pages to map > + * the entire 512GB of KVA space which is an unnecessary tax on > + * physical memory. > + */ > + pt_pages += 4; /* 8MB additional slop for kernel modules */ 8MB might be to low. I just checked one of my machines with fully modularized kernel, it takes slightly more than 6 MB to load 50 modules. I think that 16MB would be safer, but it probably needs to be scaled down based on the available phys memory. amd64 kernel could be booted on 128MB machine still.
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