Messages in this thread Patch in this message | ![/](/images/icornerl.gif) | | Date | Thu, 03 Apr 2003 16:40:20 -0600 | From | Dave McCracken <> | Subject | Re: [PATCH 2.5.66-mm3] New page_convert_anon |
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--On Thursday, April 03, 2003 14:24:41 -0800 Andrew Morton <akpm@digeo.com> wrote:
> It's more conventional to lock the page in the caller. And we forgot the > whole reason for locking it: to keep truncate away. We need to check that > the page is still on the address_space after the page lock has been > acquired. > > This applies on top of your first.
Ok, that all makes sense. Here's a patch with all your changes applied.
Dave
====================================================================== Dave McCracken IBM Linux Base Kernel Team 1-512-838-3059 dmccr@us.ibm.com T/L 678-3059 --- 2.5.66-mm3/./mm/fremap.c 2003-04-03 10:37:42.000000000 -0600 +++ 2.5.66-mm3-objfix/./mm/fremap.c 2003-04-03 16:35:27.000000000 -0600 @@ -73,7 +73,10 @@ int install_page(struct mm_struct *mm, s pgidx += vma->vm_pgoff; pgidx >>= PAGE_CACHE_SHIFT - PAGE_SHIFT; if (!PageAnon(page) && (page->index != pgidx)) { - if (page_convert_anon(page) < 0) + lock_page(page); + err = page_convert_anon(page); + unlock_page(page); + if (err < 0) goto err_free; } --- 2.5.66-mm3/./mm/rmap.c 2003-04-03 10:37:42.000000000 -0600 +++ 2.5.66-mm3-objfix/./mm/rmap.c 2003-04-03 16:36:17.000000000 -0600 @@ -460,23 +460,6 @@ void page_remove_rmap(struct page * page } } } -#ifdef DEBUG_RMAP - /* Not found. This should NEVER happen! */ - printk(KERN_ERR "page_remove_rmap: pte_chain %p not present.\n", ptep); - printk(KERN_ERR "page_remove_rmap: only found: "); - if (PageDirect(page)) { - printk("%llx", (u64)page->pte.direct); - } else { - for (pc = page->pte.chain; pc; pc = pc->next) { - int i; - for (i = 0; i < NRPTE; i++) - printk(" %d:%llx", i, (u64)pc->ptes[i]); - } - } - printk("\n"); - printk(KERN_ERR "page_remove_rmap: driver cleared PG_reserved ?\n"); -#endif - out: pte_chain_unlock(page); if (!page_mapped(page)) @@ -781,152 +764,100 @@ out: * Find all the mappings for an object-based page and convert them * to 'anonymous', ie create a pte_chain and store all the pte pointers there. * - * This function takes the address_space->i_shared_sem and the pte_chain_lock - * for the page. It jumps through some hoops to preallocate the correct number - * of pte_chain structures to ensure that it can complete without releasing - * the lock. + * This function takes the address_space->i_shared_sem, sets the PageAnon flag, + * then sets the mm->page_table_lock for each vma and calls page_add_rmap. This + * means there is a period when PageAnon is set, but still has some mappings + * with no pte_chain entry. This is in fact safe, since page_remove_rmap will + * simply not find it. try_to_unmap might erroneously return success, but it + * will never be called because the page_convert_anon() caller has locked the + * page. + * + * page_referenced() may fail to scan all the appropriate pte's and may return + * an inaccurate result. This is so rare that it does not matter. */ int page_convert_anon(struct page *page) { - struct address_space *mapping = page->mapping; + struct address_space *mapping; struct vm_area_struct *vma; - struct pte_chain *pte_chain = NULL, *ptec; + struct pte_chain *pte_chain = NULL; pte_t *pte; - pte_addr_t pte_paddr = 0; - int mapcount; - int ptecount; - int index = 1; int err = 0; + mapping = page->mapping; + if (mapping == NULL) + goto out; /* truncate won the lock_page() race */ + down(&mapping->i_shared_sem); - pte_chain_lock(page); + /* Take this only during setup */ + pte_chain_lock(page); /* * Has someone else done it for us before we got the lock? * If so, pte.direct or pte.chain has replaced pte.mapcount. */ - if (PageAnon(page)) + if (PageAnon(page)) { + pte_chain_unlock(page); goto out_unlock; + } - /* - * Preallocate the pte_chains outside the lock. - * If mapcount grows while we're allocating here, retry. - * If mapcount shrinks, we free the excess before returning. - */ - mapcount = page->pte.mapcount; - while (index < mapcount) { + SetPageAnon(page); + if (page->pte.mapcount == 0) { pte_chain_unlock(page); - up(&mapping->i_shared_sem); - for (; index < mapcount; index += NRPTE) { - if (index == 1) - index = 0; - ptec = pte_chain_alloc(GFP_KERNEL); - if (!ptec) { - err = -ENOMEM; - goto out_free; - } - ptec->next = pte_chain; - pte_chain = ptec; - } - down(&mapping->i_shared_sem); - pte_chain_lock(page); - /* - * Has someone else done it while we were allocating? - */ - if (PageAnon(page)) - goto out_unlock; - mapcount = page->pte.mapcount; + goto out_unlock; } - if (!mapcount) - goto set_anon; + /* This is gonna get incremented by page_add_rmap */ + dec_page_state(nr_mapped); + page->pte.mapcount = 0; -again: /* - * We don't try for page_table_lock (what would we do when a - * trylock fails?), therefore there's a small chance that we - * catch a vma just as it's being unmapped and its page tables - * freed. Our pte_chain_lock prevents that on vmas that really - * contain our page, but not on the others we look at. So we - * might locate junk that looks just like our page's pfn. It's - * a transient and very unlikely occurrence (much less likely - * than a trylock failing), so check how many maps we find, - * and if too many, start all over again. + * Now that the page is marked as anon, unlock it. + * page_add_rmap will lock it as necessary. */ - ptecount = 0; - ptec = pte_chain; - - /* - * Arrange for the first pte_chain to be partially filled at - * the top, and the last (and any intermediates) to be full. - */ - index = mapcount % NRPTE; - if (index) - index = NRPTE - index; + pte_chain_unlock(page); list_for_each_entry(vma, &mapping->i_mmap, shared) { if (vma->vm_pgoff > (page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT))) break; + if (!pte_chain) { + pte_chain = pte_chain_alloc(GFP_KERNEL); + if (!pte_chain) { + err = -ENOMEM; + goto out_unlock; + } + } + spin_lock(&vma->vm_mm->page_table_lock); pte = find_pte(vma, page, NULL); if (pte) { - ptecount++; - if (unlikely(ptecount > mapcount)) - goto again; - pte_paddr = ptep_to_paddr(pte); - pte_unmap(pte); - if (ptec) { - ptec->ptes[index] = pte_paddr; - index++; - if (index == NRPTE) { - ptec = ptec->next; - index = 0; - } - } + /* Make sure this isn't a duplicate */ + page_remove_rmap(page, pte); + pte_chain = page_add_rmap(page, pte, pte_chain); } + spin_unlock(&vma->vm_mm->page_table_lock); } list_for_each_entry(vma, &mapping->i_mmap_shared, shared) { if (vma->vm_pgoff > (page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT))) break; + if (!pte_chain) { + pte_chain = pte_chain_alloc(GFP_KERNEL); + if (!pte_chain) { + err = -ENOMEM; + goto out_unlock; + } + } + spin_lock(&vma->vm_mm->page_table_lock); pte = find_pte(vma, page, NULL); if (pte) { - ptecount++; - if (unlikely(ptecount > mapcount)) - goto again; - pte_paddr = ptep_to_paddr(pte); - pte_unmap(pte); - if (ptec) { - ptec->ptes[index] = pte_paddr; - index++; - if (index == NRPTE) { - ptec = ptec->next; - index = 0; - } - } + /* Make sure this isn't a duplicate */ + page_remove_rmap(page, pte); + pte_chain = page_add_rmap(page, pte, pte_chain); } + spin_unlock(&vma->vm_mm->page_table_lock); } - BUG_ON(ptecount != mapcount); - if (mapcount == 1) { - SetPageDirect(page); - page->pte.direct = pte_paddr; - /* If pte_chain is set, it's all excess to be freed */ - } else { - page->pte.chain = pte_chain; - /* Point pte_chain to any excess to be freed */ - pte_chain = ptec; - BUG_ON(index); - } - -set_anon: - SetPageAnon(page); out_unlock: - pte_chain_unlock(page); + pte_chain_free(pte_chain); up(&mapping->i_shared_sem); -out_free: - while (pte_chain) { - ptec = pte_chain->next; - pte_chain_free(pte_chain); - pte_chain = ptec; - } +out: return err; }
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