hi LKML:
I am reading kernel code about memory management.
on i386 platform, the function pgd_alloc() alloc one page table
directory,
every directory entry is one PMD address. that is OK.
pgd_t *pgd_alloc(struct mm_struct *mm)
{
int i;
pgd_t *pgd = kmem_cache_alloc(pgd_cache, GFP_KERNEL);
if (PTRS_PER_PMD == 1 || !pgd)
return pgd;
for (i = 0; i < USER_PTRS_PER_PGD; ++i) {
pmd_t *pmd = kmem_cache_alloc(pmd_cache, GFP_KERNEL);
if (!pmd)
goto out_oom;
set_pgd(&pgd[i], __pgd(1 + __pa(pmd)));
}
return pgd;
out_oom:
for (i--; i >= 0; i--)
kmem_cache_free(pmd_cache, (void *)__va(pgd_val(pgd[i])-1));
kmem_cache_free(pgd_cache, pgd);
return NULL;
}
My question is the statement:
set_pgd(&pgd[i], __pgd(1 + __pa(pmd)));
why here is not :
set_pgd(&pgd[i], __pgd(__pa(pmd)));
I can not understand this. I search intel developer mannal. but
nothing to help.
Who can tell me why?
thank in advanced.
liyu
2005/7/1
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