On Thu, Mar 17, 2016 at 12:07:44PM +0100, Vlastimil Babka wrote: > On 03/14/2016 10:40 PM, Ebru Akagunduz wrote: > >Currently khugepaged makes swapin readahead to improve > >THP collapse rate. This patch checks vm statistics > >to avoid workload of swapin, if unnecessary. So that > >when system under pressure, khugepaged won't consume > >resources to swapin. > > > >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. When waiting to swapin readahead > >left part of the test, the memory forced to be busy > >doing page reclaim. There was enough free memory during > >test, khugepaged did not swapin readahead due to business. > > > >Test results: > > > > After swapped out > >------------------------------------------------------------------- > > | Anonymous | AnonHugePages | Swap | Fraction | > >------------------------------------------------------------------- > >With patch | 206608 kB | 204800 kB | 593392 kB | %99 | > >------------------------------------------------------------------- > >Without patch | 351308 kB | 350208 kB | 448692 kB | %99 | > >------------------------------------------------------------------- > > > > After swapped in (waiting 10 minutes) > >------------------------------------------------------------------- > > | Anonymous | AnonHugePages | Swap | Fraction | > >------------------------------------------------------------------- > >With patch | 551992 kB | 368640 kB | 248008 kB | %66 | > >------------------------------------------------------------------- > >Without patch | 586816 kB | 464896 kB | 213184 kB | %79 | > >------------------------------------------------------------------- > > > >Signed-off-by: Ebru Akagunduz <[email protected]> > > Looks like a step in a good direction. Still might be worthwile to > also wait for the swapin to complete, and actually collapse > immediately, no? > I'll send a patch to solve mmap_sem issues after getting this patch series accepted. > >--- > >Changes in v2: > > - Add reference to specify which patch fixed (Ebru Akagunduz) > > The reference is again missing in v3. > > > - Fix commit subject line (Ebru Akagunduz) > > > >Changes in v3: > > - Remove default values of allocstall (Kirill A. Shutemov) > > > > mm/huge_memory.c | 13 +++++++++++-- > > 1 file changed, 11 insertions(+), 2 deletions(-) > > > >diff --git a/mm/huge_memory.c b/mm/huge_memory.c > >index 86e9666..67a398c 100644 > >--- a/mm/huge_memory.c > >+++ b/mm/huge_memory.c > >@@ -102,6 +102,7 @@ static DECLARE_WAIT_QUEUE_HEAD(khugepaged_wait); > > */ > > static unsigned int khugepaged_max_ptes_none __read_mostly; > > static unsigned int khugepaged_max_ptes_swap __read_mostly; > >+static unsigned long int allocstall; > > "int" here is unnecessary > > > > > static int khugepaged(void *none); > > static int khugepaged_slab_init(void); > >@@ -2438,7 +2439,7 @@ static void collapse_huge_page(struct mm_struct *mm, > > struct page *new_page; > > spinlock_t *pmd_ptl, *pte_ptl; > > int isolated = 0, result = 0; > >- unsigned long hstart, hend; > >+ unsigned long hstart, hend, swap, curr_allocstall; > > struct mem_cgroup *memcg; > > unsigned long mmun_start; /* For mmu_notifiers */ > > unsigned long mmun_end; /* For mmu_notifiers */ > >@@ -2493,7 +2494,14 @@ static void collapse_huge_page(struct mm_struct *mm, > > goto out; > > } > > > >- __collapse_huge_page_swapin(mm, vma, address, pmd); > >+ swap = get_mm_counter(mm, MM_SWAPENTS); > >+ curr_allocstall = sum_vm_event(ALLOCSTALL); > >+ /* > >+ * When system under pressure, don't swapin readahead. > >+ * So that avoid unnecessary resource consuming. > >+ */ > >+ if (allocstall == curr_allocstall && swap != 0) > >+ __collapse_huge_page_swapin(mm, vma, address, pmd); > > > > anon_vma_lock_write(vma->anon_vma); > > > >@@ -2790,6 +2798,7 @@ skip: > > VM_BUG_ON(khugepaged_scan.address < hstart || > > khugepaged_scan.address + HPAGE_PMD_SIZE > > > hend); > >+ allocstall = sum_vm_event(ALLOCSTALL); > > Why here? Rik said in v2: > > >Khugepaged stores the allocstall value when it goes to sleep, > >and checks it before calling (or not) __collapse_huge_page_swapin. > > But that's not true, this is not "when it goes to sleep". > So AFAICS it only observes the allocstalls between starting to scan > a single pmd, and trying to collapse the pmd. So the window is quite > tiny especially compared to I/O speeds, and this will IMHO catch > only really frequent stalls. Placing it really at "when it goes to > sleep" sounds better. > > > ret = khugepaged_scan_pmd(mm, vma, > > khugepaged_scan.address, > > hpage); > > >
