Re: [patch][rfc] 5/5: core remove PageReserved

William Lee Irwin III
2005-06-23T09:51:53Z

On Thu, Jun 23, 2005 at 05:08:24PM +1000, Nick Piggin wrote:
> @@ -337,7 +338,7 @@ static inline void get_page(struct page
> static inline void put_page(struct page *page)
> {
> - if (!PageReserved(page) && put_page_testzero(page))
> + if (put_page_testzero(page))
> __page_cache_release(page);
> }

No sweep before this? I'm not so sure.

On Thu, Jun 23, 2005 at 05:08:24PM +1000, Nick Piggin wrote:
> @@ -514,7 +534,8 @@ int copy_page_range(struct mm_struct *ds
> return 0;
> }
>
> -static void zap_pte_range(struct mmu_gather *tlb, pmd_t *pmd,
> +static void zap_pte_range(struct mmu_gather *tlb,
> + struct vm_area_struct *vma, pmd_t *pmd,
> unsigned long addr, unsigned long end,
> struct zap_details *details)
> {

As exciting as this is, !!(vma->vm_flags & VM_RESERVED) could trivially
go into struct zap_details without excess args or diff.

On Thu, Jun 23, 2005 at 05:08:24PM +1000, Nick Piggin wrote:
> @@ -1225,6 +1251,8 @@ static int do_wp_page(struct mm_struct *
> unsigned long pfn = pte_pfn(pte);
> pte_t entry;
>
> + BUG_ON(vma->vm_flags & VM_RESERVED);
> +
> if (unlikely(!pfn_valid(pfn))) {
> /*
> * This should really halt the system so it can be debugged or

!pfn_valid(pfn) is banned when !(vma->vm_flags & VM_RESERVED); here we
BUG_ON the precondition then handle !pfn_valid(pfn) in the old manner
where some new infrastructure has been erected for reporting such errors.

On Thu, Jun 23, 2005 at 05:08:24PM +1000, Nick Piggin wrote:
> @@ -1259,13 +1286,16 @@ static int do_wp_page(struct mm_struct *
> /*
> * Ok, we need to copy. Oh, well..
> */
> - if (!PageReserved(old_page))
> + if (old_page == ZERO_PAGE(address))
> + old_page = NULL;
> + else
> page_cache_get(old_page);
> +
> spin_unlock(&mm->page_table_lock);
>
> if (unlikely(anon_vma_prepare(vma)))
> goto no_new_page;
> - if (old_page == ZERO_PAGE(address)) {
> + if (old_page == NULL) {
> new_page = alloc_zeroed_user_highpage(vma, address);
> if (!new_page)
> goto no_new_page;

There are some micro-optimizations mixed in with this and some
subsequent do_wp_page() alterations.

On Thu, Jun 23, 2005 at 05:08:24PM +1000, Nick Piggin wrote:
> @@ -1654,7 +1656,7 @@ void __init memmap_init_zone(unsigned lo
>
> for (page = start; page < (start + size); page++) {
> set_page_zone(page, NODEZONE(nid, zone));
> - set_page_count(page, 0);
> + set_page_count(page, 1);
> reset_page_mapcount(page);
> SetPageReserved(page);
> INIT_LIST_HEAD(&page->lru);

The refcounting and PG_reserved activity in memmap_init_zone() is
superfluous. bootmem.c does all the necessary accounting internally.

On Thu, Jun 23, 2005 at 05:08:24PM +1000, Nick Piggin wrote:
> Index: linux-2.6/mm/fremap.c
> ===================================================================
> --- linux-2.6.orig/mm/fremap.c
> +++ linux-2.6/mm/fremap.c
> @@ -29,18 +29,21 @@ static inline void zap_pte(struct mm_str
> return;
> if (pte_present(pte)) {
> unsigned long pfn = pte_pfn(pte);
> + struct page *page;
>
> flush_cache_page(vma, addr, pfn);
> pte = ptep_clear_flush(vma, addr, ptep);
> - if (pfn_valid(pfn)) {
> - struct page *page = pfn_to_page(pfn);
> - if (!PageReserved(page)) {
> - if (pte_dirty(pte))
> - set_page_dirty(page);
> - page_remove_rmap(page);
> - page_cache_release(page);
> - dec_mm_counter(mm, rss);
> - }
> + if (unlikely(!pfn_valid(pfn))) {
> + print_invalid_pfn("zap_pte", pte, vma->vm_flags, addr);
> + return;
> + }
> + page = pfn_to_page(pfn);
> + if (page != ZERO_PAGE(addr)) {
> + if (pte_dirty(pte))
> + set_page_dirty(page);
> + page_remove_rmap(page);
> + dec_mm_counter(mm, rss);
> + page_cache_release(page);
> }
> } else {
> if (!pte_file(pte))

There is no error returned here to be handled by the caller.

On Thu, Jun 23, 2005 at 05:08:24PM +1000, Nick Piggin wrote:
> @@ -65,6 +68,8 @@ int install_page(struct mm_struct *mm, s
> pgd_t *pgd;
> pte_t pte_val;
>
> + BUG_ON(vma->vm_flags & VM_RESERVED);
> +
> pgd = pgd_offset(mm, addr);
> spin_lock(&mm->page_table_lock);
>
> @@ -122,6 +127,8 @@ int install_file_pte(struct mm_struct *m
> pgd_t *pgd;
> pte_t pte_val;
>
> + BUG_ON(vma->vm_flags & VM_RESERVED);
> +
> pgd = pgd_offset(mm, addr);
> spin_lock(&mm->page_table_lock);

This has no effect but to artificially constrain the interface. There
is no a priori reason to avoid the use of install_page() to deposit
mappings to normal pages in VM_RESERVED vmas. It's only the reverse
being "banned" here. Similar comments also apply to zap_pte().

On Thu, Jun 23, 2005 at 05:08:24PM +1000, Nick Piggin wrote:
> Index: linux-2.6/drivers/scsi/sg.c
> ===================================================================
> --- linux-2.6.orig/drivers/scsi/sg.c
> +++ linux-2.6/drivers/scsi/sg.c
> @@ -1887,9 +1887,10 @@ st_unmap_user_pages(struct scatterlist *
> int i;
>
> for (i=0; i < nr_pages; i++) {
> - if (dirtied && !PageReserved(sgl[i].page))
> + if (dirtied)
> SetPageDirty(sgl[i].page);
> /* unlock_page(sgl[i].page); */
> + /* FIXME: XXX don't dirty/unmap VM_RESERVED regions? */
> /* FIXME: cache flush missing for rw==READ
> * FIXME: call the correct reference counting function
> */

An answer should be devised for this. My numerous SCSI CD-ROM devices
(I have 5 across several different machines of several different arches)
are rather unlikely to be happy with /* FIXME: XXX ... as an answer.

On Thu, Jun 23, 2005 at 05:08:24PM +1000, Nick Piggin wrote:
> Index: linux-2.6/drivers/scsi/st.c
> ===================================================================
> --- linux-2.6.orig/drivers/scsi/st.c
> +++ linux-2.6/drivers/scsi/st.c
> @@ -4435,8 +4435,9 @@ static int sgl_unmap_user_pages(struct s
> int i;
>
> for (i=0; i < nr_pages; i++) {
> - if (dirtied && !PageReserved(sgl[i].page))
> + if (dirtied)
> SetPageDirty(sgl[i].page);
> + /* FIXME: XXX don't dirty/unmap VM_RESERVED regions? */
> /* FIXME: cache flush missing for rw==READ
> * FIXME: call the correct reference counting function
> */

Mutatis mutandis for my SCSI tape drive.

On Thu, Jun 23, 2005 at 05:08:24PM +1000, Nick Piggin wrote:
> Index: linux-2.6/sound/core/pcm_native.c
> ===================================================================
> --- linux-2.6.orig/sound/core/pcm_native.c
> +++ linux-2.6/sound/core/pcm_native.c
> @@ -2942,8 +2942,7 @@ static struct page * snd_pcm_mmap_status
> return NOPAGE_OOM;
> runtime = substream->runtime;
> page = virt_to_page(runtime->status);
> - if (!PageReserved(page))
> - get_page(page);
> + get_page(page);
> if (type)
> *type = VM_FAULT_MINOR;
> return page;

snd_malloc_pages() marks all pages it allocates PG_reserved. This
merits some commentary, and likely the removal of the superfluous
PG_reserved usage.

On Thu, Jun 23, 2005 at 05:08:24PM +1000, Nick Piggin wrote:
> Index: linux-2.6/mm/mmap.c
> ===================================================================
> --- linux-2.6.orig/mm/mmap.c
> +++ linux-2.6/mm/mmap.c
> @@ -1073,6 +1073,17 @@ munmap_back:
> error = file->f_op->mmap(file, vma);
> if (error)
> goto unmap_and_free_vma;
> + if ((vma->vm_flags & (VM_SHARED | VM_WRITE | VM_RESERVED))
> + == (VM_WRITE | VM_RESERVED)) {
> + printk(KERN_WARNING "program %s is using MAP_PRIVATE, "
> + "PROT_WRITE mmap of VM_RESERVED memory, which "
> + "is deprecated. Please report this to "
> + "linux-kernel@vger.kernel.org\n",current->comm);
> + if (vma->vm_ops && vma->vm_ops->close)
> + vma->vm_ops->close(vma);
> + error = -EACCES;
> + goto unmap_and_free_vma;
> + }
> } else if (vm_flags & VM_SHARED) {
> error = shmem_zero_setup(vma);
> if (error)

This is user-triggerable where the driver honors mmap() protection
flags blindly.

On Thu, Jun 23, 2005 at 05:08:24PM +1000, Nick Piggin wrote:
> Index: linux-2.6/mm/bootmem.c
> ===================================================================
> --- linux-2.6.orig/mm/bootmem.c
> +++ linux-2.6/mm/bootmem.c
> @@ -286,6 +286,7 @@ static unsigned long __init free_all_boo
> if (j + 16 < BITS_PER_LONG)
> prefetchw(page + j + 16);
> __ClearPageReserved(page + j);
> + set_page_count(page + j, 0);
> }
> __free_pages(page, order);
> i += BITS_PER_LONG;

ibid re: bootmem

On Thu, Jun 23, 2005 at 05:08:24PM +1000, Nick Piggin wrote:
> Index: linux-2.6/kernel/power/swsusp.c
> ===================================================================
> --- linux-2.6.orig/kernel/power/swsusp.c
> +++ linux-2.6/kernel/power/swsusp.c
> @@ -433,15 +433,12 @@ static int save_highmem_zone(struct zone
> continue;
> page = pfn_to_page(pfn);
> /*
> + * PageReserved(page) -
> * This condition results from rvmalloc() sans vmalloc_32()
> * and architectural memory reservations. This should be
> * corrected eventually when the cases giving rise to this
> * are better understood.
> */
> - if (PageReserved(page)) {
> - printk("highmem reserved page?!\n");
> - continue;
> - }
> BUG_ON(PageNosave(page));
> if (PageNosaveFree(page))
> continue;

This behavioral change needs to be commented on. There are some additional
difficulties when memory holes are unintentionally covered by mem_map[];
It is beneficial otherwise. It's likely to triplefault on such holes.

On Thu, Jun 23, 2005 at 05:08:24PM +1000, Nick Piggin wrote:
> @@ -527,13 +524,8 @@ static int saveable(struct zone * zone,
> return 0;
>
> page = pfn_to_page(pfn);
> - BUG_ON(PageReserved(page) && PageNosave(page));
> if (PageNosave(page))
> return 0;
> - if (PageReserved(page) && pfn_is_nosave(pfn)) {
> - pr_debug("[nosave pfn 0x%lx]", pfn);
> - return 0;
> - }
> if (PageNosaveFree(page))
> return 0;

The pfn_is_nosave() check must stand barring justification of why
unintentionally saving (and hence restoring) the page is tolerable.

-- wli