Messages in this thread | | | Date | Tue, 14 Oct 2003 11:08:26 +0200 | From | Hans Berglund <> | Subject | Kernel memory allocation and page used counter |
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I have reserved a bounch of 128k sized pieces of kernel memory using addr[i] = __get_free_pages (GFP_KERNEL, 5); repeated times.
The first time the pages are used, I can DMA to this memory, and get the data without problems. After freeing the memory with free_pages (addr[i], 5); and allocating next time, the kernel crashes in different ways each time when I use the memory. Usually an oops with the message: "Unable to handle kernel paging request at virtual address xxxxxxxx".
I have noticed that the struct page->count.counter of the first page of each 128k chunk is incremented, but not of the remaining pages. Then I tried to increment the counter "manually" by using get_page() just after allocation, and the system seemed to become stable.
Do I really have to mark the pages as used, just after allocation, and is there a kernel call to du this in one operation? If the pages are used by others, why does the kernel crash after the second allocation, and not the first?
I am running kernel 2.4.19, and I use the code below to do the mapping.
All answers are appreciated.
Hans
struct page *xxx_vma_nopage (struct vm_area_struct *vma, unsigned long addr, int write) { int offset, block; void *virt_addr; card_t *cp; struct page *cpage;
cp = vma->vm_private_data; offset = addr - vma->vm_start; if ((addr < vma->vm_start) || (addr >= vma->vm_end)) { PWARNING ("nopage: Mapping out of range, start=0x%x, addr=0x%x," "end=0x%x\n", (int)vma->vm_start, (int)addr, (int)vma->vm_end); return (0); } block = offset / KM_SIZE; /* KM_SIZE = 128k */ virt_addr = cp->list[block].address + (offset % KM_SIZE); cpage = virt_to_page (virt_addr); get_page (cpage); return (cpage); }
struct vm_operations_struct xxx_vmops = { open: xxx_vma_open, close: xxx_vma_close, nopage: xxx_vma_nopage, };
int xxx_mmap (struct file *filp, struct vm_area_struct *vma) { card_t *cp = &xxxarr[MINOR(filp->f_dentry->d_inode->i_rdev)]; vma->vm_flags |= VM_RESERVED;
vma->vm_ops = &xxx_vmops; vma->vm_private_data = cp; xxx_vma_open(vma); return (0); }
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