On Mon, May 23, 2016 at 08:14:11PM +0300, Ebru Akagunduz wrote: > Currently khugepaged makes swapin readahead under > down_write. This patch supplies to make swapin > readahead under down_read instead of down_write. > > The patch was tested with a test program that allocates > 800MB of memory, writes to it, and then sleeps. The system > was forced to swap out all. Afterwards, the test program > touches the area by writing, it skips a page in each > 20 pages of the area. > > Signed-off-by: Ebru Akagunduz <ebru.akagun...@gmail.com> > --- > mm/huge_memory.c | 33 +++++++++++++++++++++++++++------ > 1 file changed, 27 insertions(+), 6 deletions(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index feee44c..668bc07 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -2386,13 +2386,14 @@ static bool hugepage_vma_check(struct vm_area_struct > *vma) > * but with mmap_sem held to protect against vma changes. > */ > > -static void __collapse_huge_page_swapin(struct mm_struct *mm, > +static bool __collapse_huge_page_swapin(struct mm_struct *mm, > struct vm_area_struct *vma, > unsigned long address, pmd_t *pmd) > { > unsigned long _address; > pte_t *pte, pteval; > int swapped_in = 0, ret = 0; > + struct vm_area_struct *vma_orig = vma; > > pte = pte_offset_map(pmd, address); > for (_address = address; _address < address + HPAGE_PMD_NR*PAGE_SIZE; > @@ -2402,11 +2403,19 @@ static void __collapse_huge_page_swapin(struct > mm_struct *mm, > continue; > swapped_in++; > ret = do_swap_page(mm, vma, _address, pte, pmd, > - > FAULT_FLAG_ALLOW_RETRY|FAULT_FLAG_RETRY_NOWAIT, > + FAULT_FLAG_ALLOW_RETRY, > pteval); > + /* do_swap_page returns VM_FAULT_RETRY with released mmap_sem */ > + if (ret & VM_FAULT_RETRY) { > + down_read(&mm->mmap_sem); > + vma = find_vma(mm, address); > + /* vma is no longer available, don't continue to swapin > */ > + if (vma != vma_orig) > + return false; > + } > if (ret & VM_FAULT_ERROR) { > trace_mm_collapse_huge_page_swapin(mm, swapped_in, 0); > - return; > + return false; > } > /* pte is unmapped now, we need to map it */ > pte = pte_offset_map(pmd, _address); > @@ -2414,6 +2423,7 @@ static void __collapse_huge_page_swapin(struct > mm_struct *mm, > pte--; > pte_unmap(pte); > trace_mm_collapse_huge_page_swapin(mm, swapped_in, 1); > + return true; > } > > static void collapse_huge_page(struct mm_struct *mm, > @@ -2459,7 +2469,7 @@ static void collapse_huge_page(struct mm_struct *mm, > * gup_fast later hanlded by the ptep_clear_flush and the VM > * handled by the anon_vma lock + PG_lock. > */ > - down_write(&mm->mmap_sem); > + down_read(&mm->mmap_sem); > if (unlikely(khugepaged_test_exit(mm))) { > result = SCAN_ANY_PROCESS; > goto out; > @@ -2490,9 +2500,20 @@ static void collapse_huge_page(struct mm_struct *mm, > * Don't perform swapin readahead when the system is under pressure, > * to avoid unnecessary resource consumption. > */ > - if (allocstall == curr_allocstall && swap != 0) > - __collapse_huge_page_swapin(mm, vma, address, pmd); > + if (allocstall == curr_allocstall && swap != 0) { > + /* > + * __collapse_huge_page_swapin always returns with mmap_sem > + * locked. If it fails, release mmap_sem and jump directly > + * label out. Continuing to collapse causes inconsistency. > + */ > + if (!__collapse_huge_page_swapin(mm, vma, address, pmd)) { > + up_read(&mm->mmap_sem); > + goto out; > + } > + } > > + up_read(&mm->mmap_sem); > + down_write(&mm->mmap_sem);
That's the critical point. How do you guarantee that the vma will not be destroyed (or changed) between up_read() and down_write()? You need at least find_vma() again. > anon_vma_lock_write(vma->anon_vma); > > pte = pte_offset_map(pmd, address); > -- > 1.9.1 > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majord...@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"d...@kvack.org"> em...@kvack.org </a> -- Kirill A. Shutemov