Hi:
I am working on a project to copy (page aligned) the buffer content of one
process to the buffer of other process.
Now I resolved this issue using copy_page() but, analizing performance with
different buffer sizes, the "copy_page" becames the critical time component and
limiting factor.
I read some articles about, COW, zero copy and page flipping and I wrote a
kernel code to implement page "transfer" (only copy page references), but that
code fail and hang. The kernel I use is 2.6.32.
The pseudocode I think is:
pte_t *src_pte, *dst_pte;
src_pte = getpte(src_task);
dst_pte = getpte(dst_task);
free_pte(dst_pte); /*to free the page referenced by this PTE */
*dst_pte = *src_pte; /*copy source PTE to destination PTE */
And here is code added to the kernel:
-------------------------------------------------------------------------------------------------------------
len = PAGE_SIZE;
src_vma=find_vma_intersection(src_proc->p_task->mm,src_addr,src_addr+len);
dst_vma=find_vma_intersection(dst_proc->p_task->mm,dst_addr,dst_addr+len);
src_pgd=pgd_offset(src_proc->p_task->mm, (unsigned long) src_addr);
src_pud=pud_offset(src_pgd,(unsigned long) src_addr);
src_pmd=pmd_offset(src_pud,(unsigned long) src_addr);
src_pte=pte_offset_map_lock(src_proc->p_task->mm, src_pmd,(unsigned long)
src_addr, &src_ptl);
dst_pgd=pgd_offset(dst_proc->p_task->mm, (unsigned long) dst_addr);
dst_pud=pud_offset(dst_pgd,(unsigned long) dst_addr);
dst_pmd=pmd_offset(dst_pud,(unsigned long) dst_addr);
dst_pte=pte_offset_map_lock(dst_proc->p_task->mm, dst_pmd,(unsigned long)
dst_addr, &dst_ptl);
pte_free(dst_proc->p_task->mm, dst_pte);
copy_pte_range(dst_proc->p_task->mm, src_proc->p_task->mm, dst_pmd, src_pmd,
dst_vma, (unsigned long) dst_addr, ((unsigned
long)dst_addr+PAGE_SIZE));
spin_unlock(src_ptl);
spin_unlock(dst_ptl);
-------------------------------------------------------------------------------------------------------------
There are a lots of kernel functions that are not well documented or they have
been changed.
Can anybody help me with this issue? Does COW (Copy On Write) will make the
copy when the processes will modify their buffers?
I am not suscribed to the mailing list, please CC: the answers to this email
account.
Thanks in Advance.
I apologize for my basic English.
Pablo Pessolani
PD: once finishing with that code, some issues about page protection will be
considered.
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