Re: [PATCH 2.6.16.29 1/1] memory: enhance Linux swap subsystem

From: zyf.zeroos
Date: Fri Jan 05 2007 - 18:11:56 EST


Test mail with my signature, mail content is based on the second quilt patch (Linux 2.6.16.29), only two key files are re-sent 1) Documentation/vm_pps.txt 2) mm/vmscan.c

Index: test.signature/Documentation/vm_pps.txt
===================================================================
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ test.signature/Documentation/vm_pps.txt 2007-01-06 07:00:18.146480584 +0800
@@ -0,0 +1,214 @@
+ Pure Private Page System (pps)
+ Copyright by Yunfeng Zhang on GFDL 1.2
+ zyf.zeroos@xxxxxxxxx
+ December 24-26, 2006
+
+// Purpose <([{
+The file is used to document the idea which is published firstly at
+http://www.ussg.iu.edu/hypermail/linux/kernel/0607.2/0451.html, as a part of my
+OS -- main page http://blog.chinaunix.net/u/21764/index.php. In brief, the
+patch of the document is for enchancing the performance of Linux swap
+subsystem. You can find the overview of the idea in section <How to Reclaim
+Pages more Efficiently> and how I patch it into Linux 2.6.16.29 in section
+<Pure Private Page System -- pps>.
+// }])>
+
+// How to Reclaim Pages more Efficiently <([{
+Good idea originates from overall design and management ability, when you look
+down from a manager view, you will relief yourself from disordered code and
+find some problem immediately.
+
+OK! to modern OS, its memory subsystem can be divided into three layers
+1) Space layer (InodeSpace, UserSpace and CoreSpace).
+2) VMA layer (PrivateVMA and SharedVMA, memory architecture-independent layer).
+3) PTE, zone/memory inode layer (architecture-dependent).
+4) Maybe it makes you sense that Page should be placed on the 3rd layer, but
+ here, it's placed on the 2nd layer since it's the basic unit of VMA.
+
+Since the 2nd layer assembles the much statistic of page-acess information, so
+it's nature that swap subsystem should be deployed and implemented on the 2nd
+layer.
+
+Undoubtedly, there are some virtues about it
+1) SwapDaemon can collect the statistic of process acessing pages and by it
+ unmaps ptes, SMP specially benefits from it for we can use flush_tlb_range
+ to unmap ptes batchly rather than frequently TLB IPI interrupt per a page in
+ current Linux legacy swap subsystem.
+2) Page-fault can issue better readahead requests since history data shows all
+ related pages have conglomerating affinity. In contrast, Linux page-fault
+ readaheads the pages relative to the SwapSpace position of current
+ page-fault page.
+3) It's conformable to POSIX madvise API family.
+
+Unfortunately, Linux 2.6.16.29 swap subsystem is based on the 3rd layer -- a
+system on zone::active_list/inactive_list.
+
+I've finished a patch, see section <Pure Private Page System -- pps>. Note, it
+ISN'T perfect.
+// }])>
+
+// Pure Private Page System -- pps <([{
+As I've referred in previous section, perfectly applying my idea need to unroot
+page-surrounging swap subsystem to migrate it on VMA, but a huge gap has
+defeated me -- active_list and inactive_list. In fact, you can find
+lru_add_active code anywhere ... It's IMPOSSIBLE to me to complete it only by
+myself. It's also the difference between my design and Linux, in my OS, page is
+the charge of its new owner totally, however, to Linux, page management system
+is still tracing it by PG_active flag.
+
+So I conceive another solution:) That is, set up an independent page-recycle
+system rooted on Linux legacy page system -- pps, intercept all private pages
+belonging to PrivateVMA to pps, then use my pps to cycle them. By the way, the
+whole job should be consist of two parts, here is the first --
+PrivateVMA-oriented (PPS), other is SharedVMA-oriented (should be called SPS)
+scheduled in future. Of course, if all are done, it will empty Linux legacy
+page system.
+
+In fact, pps is centered on how to better collect and unmap process private
+pages in SwapDaemon mm/vmscan.c:shrink_private_vma, the whole process is
+divided into six stages -- <Stage Definition>. Other sections show the remain
+aspects of pps
+1) <Data Definition> is basic data definition.
+2) <Concurrent racers of Shrinking pps> is focused on synchronization.
+3) <Private Page Lifecycle of pps> -- how private pages enter in/go off pps.
+4) <VMA Lifecycle of pps> which VMA is belonging to pps.
+
+PPS uses init_mm.mm_list list to enumerate all swappable UserSpace
+(shrink_private_vma).
+
+A new kernel thread -- kppsd is introduced in mm/vmscan.c, its task is to
+execute the stages of pps periodically, note an appropriate timeout ticks is
+necessary so we can give application a chance to re-map back its PrivatePage
+from UnmappedPTE to PTE, that is, show their conglomeration affinity.
+scan_control::pps_cmd field is used to control the behavior of kppsd, = 1 for
+accelerating scanning process and reclaiming pages, it's used in balance_pgdat.
+
+PPS statistic data is appended to /proc/meminfo entry, its prototype is in
+include/linux/mm.h.
+
+I'm also glad to highlight my a new idea -- dftlb which is described in
+section <Delay to Flush TLB>.
+// }])>
+
+// Delay to Flush TLB (dftlb) <([{
+Delay to flush TLB is instroduced by me to enhance flushing TLB efficiency, in
+brief, when we want to unmap a page from the page table of a process, why we
+send TLB IPI to other CPUs immediately, since every CPU has timer interrupt, we
+can insert flushing tasks into timer interrupt route to implement a
+free-charged TLB flushing.
+
+The trick is implemented in
+1) TLB flushing task is added in fill_in_tlb_task of mm/vmscan.c.
+2) timer_flush_tlb_tasks of kernel/timer.c is used by other CPUs to execute
+ flushing tasks.
+3) all data are defined in include/linux/mm.h.
+
+The restriction of dftlb. Following conditions must be met
+1) atomic cmpxchg instruction.
+2) atomically set the access bit after they touch a pte firstly.
+3) To some architectures, vma parameter of flush_tlb_range is maybe important,
+ if it's true, since it's possible that the vma of a TLB flushing task has
+ gone when a CPU starts to execute the task in timer interrupt, so don't use
+ dftlb.
+combine stage 1 with stage 2, and send IPI immediately in fill_in_tlb_tasks.
+
+dftlb increases mm_struct::mm_users to prevent the mm from being freed when
+other CPU works on it.
+// }])>
+
+// Stage Definition <([{
+The whole process of private page page-out is divided into six stages, as
+showed in shrink_pvma_scan_ptes of mm/vmscan.c, the code groups the similar
+pages to a series.
+1) PTE to untouched PTE (access bit is cleared), append flushing tasks to dftlb.
+2) Convert untouched PTE to UnmappedPTE.
+3) Link SwapEntry to every UnmappedPTE.
+4) Flush PrivatePage of UnmappedPTE to its disk SwapPage.
+5) Reclaimed the page and shift UnmappedPTE to SwappedPTE.
+6) SwappedPTE stage.
+// }])>
+
+// Data Definition <([{
+New VMA flag (VM_PURE_PRIVATE) is appended into VMA in include/linux/mm.h.
+
+New PTE type (UnmappedPTE) is appended into PTE system in
+include/asm-i386/pgtable.h. Its prototype is
+struct UnmappedPTE {
+ int present : 1; // must be 0.
+ ...
+ int pageNum : 20;
+};
+The new PTE has a feature, it keeps a link to its PrivatePage and prevent the
+page from being visited by CPU, so you can use it in <Stage Definition> as a
+middleware.
+// }])>
+
+// Concurrent Racers of Shrinking pps <([{
+shrink_private_vma of mm/vmscan.c uses init_mm.mmlist to scan all swappable
+mm_struct instances, during the process of scaning and reclaiming process, it
+readlockes every mm_struct object, which brings some potential concurrent
+racers
+1) mm/swapfile.c pps_swapoff (swapoff API).
+2) mm/memory.c do_wp_page, handle_pte_fault::unmapped_pte, do_anonymous_page
+ (page-fault).
+
+The VMAs of pps can coexist with madvise, mlock, mprotect, mmap and munmap,
+that is why new VMA created from mmap.c:split_vma can re-enter into pps.
+// }])>
+
+// Private Page Lifecycle of pps <([{
+All pages belonging to pps are called as pure private page, its PTE type is PTE
+or UnmappedPTE.
+
+IN (NOTE, when a pure private page enters into pps, it's also trimmed from
+Linux legacy page system by commeting lru_cache_add_active clause)
+1) fs/exec.c install_arg_pages (argument pages).
+2) mm/memory do_anonymous_page, do_wp_page, do_swap_page (page fault).
+3) mm/swap_state.c read_swap_cache_async (swap pages).
+
+OUT
+1) mm/vmscan.c shrink_pvma_scan_ptes (stage 6, reclaim a private page).
+2) mm/memory zap_pte_range (free a page).
+3) kernel/fork.c dup_mmap (if someone uses fork, migrate all pps pages
+ back to let Linux legacy page system manage them).
+
+When a pure private page is in pps, it can be visited simultaneously by
+page-fault and SwapDaemon.
+// }])>
+
+// VMA Lifecycle of pps <([{
+When a PrivateVMA enters into pps, it's or-ed a new flag -- VM_PURE_PRIVATE in
+memory.c:enter_pps, you can also find which VMA is fit with pps in it, the flag
+is used in the shrink_private_vma of mm/vmscan.c. Other fields are left
+untouched.
+
+IN.
+1) fs/exec.c setup_arg_pages (StackVMA).
+2) mm/mmap.c do_mmap_pgoff, do_brk (DataVMA).
+3) mm/mmap.c split_vma, copy_vma (in some cases, we need copy a VMA from an
+ exist VMA).
+
+OUT.
+1) kernel/fork.c dup_mmap (if someone uses fork, return the vma back to
+ Linux legacy system).
+2) mm/mmap.c remove_vma, vma_adjust (destroy VMA).
+3) mm/mmap.c do_mmap_pgoff (delete VMA when some errors occur).
+// }])>
+
+// Postscript <([{
+Note, some circumstances aren't tested due to hardware restriction e.g. SMP
+dftlb.
+
+Here are some improvements about pps
+1) In fact, I recommend one-to-one private model -- PrivateVMA, (PTE,
+ UnmappedPTE) and PrivatePage (SwapPage) which is described in my OS and the
+ aboved hyperlink of Linux kernel mail list. So it's a compromise to use
+ Linux legacy SwapCache in my pps.
+2) SwapSpace should provide more flexible interfaces, shrink_pvma_scan_ptes
+ need allocate swap entries in batch, exactly, allocate a batch of fake
+ continual swap entries, see mm/pps_swapin_readahead.
+
+If Linux kernel group can't make a schedule to re-write their memory code,
+however, pps maybe is the best solution until now.
+// }])>
+// vim: foldmarker=<([{,}])> foldmethod=marker et
Index: test.signature/mm/vmscan.c
===================================================================
--- test.signature.orig/mm/vmscan.c 2007-01-06 07:00:11.799445480 +0800
+++ test.signature/mm/vmscan.c 2007-01-06 07:00:23.326693072 +0800
@@ -79,6 +79,9 @@
* In this context, it doesn't matter that we scan the
* whole list at once. */
int swap_cluster_max;
+
+ /* pps control command, 0: do stage 1-4, kppsd only; 1: full stages. */
+ int pps_cmd;
};

/*
@@ -1514,6 +1517,428 @@
return ret;
}

+// pps fields.
+static wait_queue_head_t kppsd_wait;
+static struct scan_control wakeup_sc;
+struct pps_info pps_info = {
+ .total = ATOMIC_INIT(0),
+ .pte_count = ATOMIC_INIT(0), // stage 1 and 2.
+ .unmapped_count = ATOMIC_INIT(0), // stage 3 and 4.
+ .swapped_count = ATOMIC_INIT(0) // stage 6.
+};
+// pps end.
+
+struct series_t {
+ pte_t orig_ptes[MAX_SERIES_LENGTH];
+ pte_t* ptes[MAX_SERIES_LENGTH];
+ struct page* pages[MAX_SERIES_LENGTH];
+ int series_length;
+ int series_stage;
+} series;
+
+static int get_series_stage(pte_t* pte, int index)
+{
+ series.orig_ptes[index] = *pte;
+ series.ptes[index] = pte;
+ if (pte_present(series.orig_ptes[index])) {
+ struct page* page = pfn_to_page(pte_pfn(series.orig_ptes[index]));
+ series.pages[index] = page;
+ if (page == ZERO_PAGE(addr)) // reserved page is exclusive from us.
+ return 7;
+ if (pte_young(series.orig_ptes[index])) {
+ return 1;
+ } else
+ return 2;
+ } else if (pte_unmapped(series.orig_ptes[index])) {
+ struct page* page = pfn_to_page(pte_pfn(series.orig_ptes[index]));
+ series.pages[index] = page;
+ if (!PageSwapCache(page))
+ return 3;
+ else {
+ if (PageWriteback(page) || PageDirty(page))
+ return 4;
+ else
+ return 5;
+ }
+ } else // pte_swapped -- SwappedPTE
+ return 6;
+}
+
+static void find_series(pte_t** start, unsigned long* addr, unsigned long end)
+{
+ int i;
+ int series_stage = get_series_stage((*start)++, 0);
+ *addr += PAGE_SIZE;
+
+ for (i = 1; i < MAX_SERIES_LENGTH && *addr < end; i++, (*start)++, *addr += PAGE_SIZE) {
+ if (series_stage != get_series_stage(*start, i))
+ break;
+ }
+ series.series_stage = series_stage;
+ series.series_length = i;
+}
+
+struct delay_tlb_task delay_tlb_tasks[32] = { [0 ... 31] = {0} };
+
+void timer_flush_tlb_tasks(void* data)
+{
+ int i;
+#ifdef CONFIG_X86
+ int flag = 0;
+#endif
+ for (i = 0; i < 32; i++) {
+ if (delay_tlb_tasks[i].mm != NULL &&
+ cpu_isset(smp_processor_id(), delay_tlb_tasks[i].mm->cpu_vm_mask) &&
+ cpu_isset(smp_processor_id(), delay_tlb_tasks[i].cpu_mask)) {
+#ifdef CONFIG_X86
+ flag = 1;
+#elif
+ // smp::local_flush_tlb_range(delay_tlb_tasks[i]);
+#endif
+ cpu_clear(smp_processor_id(), delay_tlb_tasks[i].cpu_mask);
+ }
+ }
+#ifdef CONFIG_X86
+ if (flag)
+ local_flush_tlb();
+#endif
+}
+
+static struct delay_tlb_task* delay_task = NULL;
+static int vma_index = 0;
+
+static struct delay_tlb_task* search_free_tlb_tasks_slot(void)
+{
+ struct delay_tlb_task* ret = NULL;
+ int i;
+again:
+ for (i = 0; i < 32; i++) {
+ if (delay_tlb_tasks[i].mm != NULL) {
+ if (cpus_empty(delay_tlb_tasks[i].cpu_mask)) {
+ mmput(delay_tlb_tasks[i].mm);
+ delay_tlb_tasks[i].mm = NULL;
+ ret = &delay_tlb_tasks[i];
+ }
+ } else
+ ret = &delay_tlb_tasks[i];
+ }
+ if (!ret) { // Force flush TLBs.
+ on_each_cpu(timer_flush_tlb_tasks, NULL, 0, 1);
+ goto again;
+ }
+ return ret;
+}
+
+static void init_delay_task(struct mm_struct* mm)
+{
+ cpus_clear(delay_task->cpu_mask);
+ vma_index = 0;
+ delay_task->mm = mm;
+}
+
+/*
+ * We will be working on the mm, so let's force to flush it if necessary.
+ */
+static void start_tlb_tasks(struct mm_struct* mm)
+{
+ int i, flag = 0;
+again:
+ for (i = 0; i < 32; i++) {
+ if (delay_tlb_tasks[i].mm == mm) {
+ if (cpus_empty(delay_tlb_tasks[i].cpu_mask)) {
+ mmput(delay_tlb_tasks[i].mm);
+ delay_tlb_tasks[i].mm = NULL;
+ } else
+ flag = 1;
+ }
+ }
+ if (flag) { // Force flush TLBs.
+ on_each_cpu(timer_flush_tlb_tasks, NULL, 0, 1);
+ goto again;
+ }
+ BUG_ON(delay_task != NULL);
+ delay_task = search_free_tlb_tasks_slot();
+ init_delay_task(mm);
+}
+
+static void end_tlb_tasks(void)
+{
+ atomic_inc(&delay_task->mm->mm_users);
+ delay_task->cpu_mask = delay_task->mm->cpu_vm_mask;
+ delay_task = NULL;
+#ifndef CONFIG_SMP
+ timer_flush_tlb_tasks(NULL);
+#endif
+}
+
+static void fill_in_tlb_tasks(struct vm_area_struct* vma, unsigned long addr,
+ unsigned long end)
+{
+ struct mm_struct* mm;
+ // First, try to combine the task with the previous.
+ if (vma_index != 0 && delay_task->vma[vma_index - 1] == vma &&
+ delay_task->end[vma_index - 1] == addr) {
+ delay_task->end[vma_index - 1] = end;
+ return;
+ }
+fill_it:
+ if (vma_index != 32) {
+ delay_task->vma[vma_index] = vma;
+ delay_task->start[vma_index] = addr;
+ delay_task->end[vma_index] = end;
+ vma_index++;
+ return;
+ }
+ mm = delay_task->mm;
+ end_tlb_tasks();
+
+ delay_task = search_free_tlb_tasks_slot();
+ init_delay_task(mm);
+ goto fill_it;
+}
+
+static void shrink_pvma_scan_ptes(struct scan_control* sc, struct mm_struct*
+ mm, struct vm_area_struct* vma, pmd_t* pmd, unsigned long addr,
+ unsigned long end)
+{
+ int i, statistic;
+ spinlock_t* ptl = pte_lockptr(mm, pmd);
+ pte_t* pte = pte_offset_map(pmd, addr);
+ int anon_rss = 0;
+ struct pagevec freed_pvec;
+ int may_enter_fs = (sc->gfp_mask & (__GFP_FS | __GFP_IO));
+ struct address_space* mapping = &swapper_space;
+
+ pagevec_init(&freed_pvec, 1);
+ do {
+ memset(&series, 0, sizeof(struct series_t));
+ find_series(&pte, &addr, end);
+ if (sc->pps_cmd == 0 && series.series_stage == 5)
+ continue;
+ switch (series.series_stage) {
+ case 1: // PTE -- untouched PTE.
+ for (i = 0; i < series.series_length; i++) {
+ struct page* page = series.pages[i];
+ lock_page(page);
+ spin_lock(ptl);
+ if (unlikely(pte_same(*series.ptes[i], series.orig_ptes[i]))) {
+ if (pte_dirty(*series.ptes[i]))
+ set_page_dirty(page);
+ set_pte_at(mm, addr + i * PAGE_SIZE, series.ptes[i],
+ pte_mkold(pte_mkclean(*series.ptes[i])));
+ }
+ spin_unlock(ptl);
+ unlock_page(page);
+ }
+ fill_in_tlb_tasks(vma, addr, addr + (PAGE_SIZE * series.series_length));
+ break;
+ case 2: // untouched PTE -- UnmappedPTE.
+ /*
+ * Note in stage 1, we've flushed TLB in fill_in_tlb_tasks, so
+ * if it's still clear here, we can shift it to Unmapped type.
+ *
+ * If some architecture doesn't support atomic cmpxchg
+ * instruction or can't atomically set the access bit after
+ * they touch a pte at first, combine stage 1 with stage 2, and
+ * send IPI immediately in fill_in_tlb_tasks.
+ */
+ spin_lock(ptl);
+ statistic = 0;
+ for (i = 0; i < series.series_length; i++) {
+ if (unlikely(pte_same(*series.ptes[i], series.orig_ptes[i]))) {
+ pte_t pte_unmapped = series.orig_ptes[i];
+ pte_unmapped.pte_low &= ~_PAGE_PRESENT;
+ pte_unmapped.pte_low |= _PAGE_UNMAPPED;
+ if (cmpxchg(&series.ptes[i]->pte_low,
+ series.orig_ptes[i].pte_low,
+ pte_unmapped.pte_low) !=
+ series.orig_ptes[i].pte_low)
+ continue;
+ page_remove_rmap(series.pages[i]);
+ anon_rss--;
+ statistic++;
+ }
+ }
+ atomic_add(statistic, &pps_info.unmapped_count);
+ atomic_sub(statistic, &pps_info.pte_count);
+ spin_unlock(ptl);
+ break;
+ case 3: // Attach SwapPage to PrivatePage.
+ /*
+ * A better arithmetic should be applied to Linux SwapDevice to
+ * allocate fake continual SwapPages which are close to each
+ * other, the offset between two close SwapPages is less than 8.
+ */
+ if (sc->may_swap) {
+ for (i = 0; i < series.series_length; i++) {
+ lock_page(series.pages[i]);
+ if (!PageSwapCache(series.pages[i])) {
+ if (!add_to_swap(series.pages[i], GFP_ATOMIC)) {
+ unlock_page(series.pages[i]);
+ break;
+ }
+ }
+ unlock_page(series.pages[i]);
+ }
+ }
+ break;
+ case 4: // SwapPage isn't consistent with PrivatePage.
+ /*
+ * A mini version pageout().
+ *
+ * Current swap space can't commit multiple pages together:(
+ */
+ if (sc->may_writepage && may_enter_fs) {
+ for (i = 0; i < series.series_length; i++) {
+ struct page* page = series.pages[i];
+ int res;
+
+ if (!may_write_to_queue(mapping->backing_dev_info))
+ break;
+ lock_page(page);
+ if (!PageDirty(page) || PageWriteback(page)) {
+ unlock_page(page);
+ continue;
+ }
+ clear_page_dirty_for_io(page);
+ struct writeback_control wbc = {
+ .sync_mode = WB_SYNC_NONE,
+ .nr_to_write = SWAP_CLUSTER_MAX,
+ .nonblocking = 1,
+ .for_reclaim = 1,
+ };
+ page_cache_get(page);
+ SetPageReclaim(page);
+ res = swap_writepage(page, &wbc);
+ if (res < 0) {
+ handle_write_error(mapping, page, res);
+ ClearPageReclaim(page);
+ page_cache_release(page);
+ break;
+ }
+ if (!PageWriteback(page))
+ ClearPageReclaim(page);
+ page_cache_release(page);
+ }
+ }
+ break;
+ case 5: // UnmappedPTE -- SwappedPTE, reclaim PrivatePage.
+ statistic = 0;
+ for (i = 0; i < series.series_length; i++) {
+ struct page* page = series.pages[i];
+ lock_page(page);
+ spin_lock(ptl);
+ if (unlikely(!pte_same(*series.ptes[i], series.orig_ptes[i]))) {
+ spin_unlock(ptl);
+ unlock_page(page);
+ continue;
+ }
+ statistic++;
+ swp_entry_t entry = { .val = page_private(page) };
+ swap_duplicate(entry);
+ pte_t pte_swp = swp_entry_to_pte(entry);
+ set_pte_at(mm, addr + i * PAGE_SIZE, series.ptes[i], pte_swp);
+ spin_unlock(ptl);
+ if (PageSwapCache(page) && !PageWriteback(page))
+ delete_from_swap_cache(page);
+ unlock_page(page);
+
+ if (!pagevec_add(&freed_pvec, page))
+ __pagevec_release_nonlru(&freed_pvec);
+ sc->nr_reclaimed++;
+ }
+ atomic_add(statistic, &pps_info.swapped_count);
+ atomic_sub(statistic, &pps_info.unmapped_count);
+ atomic_sub(statistic, &pps_info.total);
+ break;
+ case 6:
+ // NULL operation!
+ break;
+ }
+ } while (addr < end);
+ add_mm_counter(mm, anon_rss, anon_rss);
+ if (pagevec_count(&freed_pvec))
+ __pagevec_release_nonlru(&freed_pvec);
+}
+
+static void shrink_pvma_pmd_range(struct scan_control* sc, struct mm_struct*
+ mm, struct vm_area_struct* vma, pud_t* pud, unsigned long addr,
+ unsigned long end)
+{
+ unsigned long next;
+ pmd_t* pmd = pmd_offset(pud, addr);
+ do {
+ next = pmd_addr_end(addr, end);
+ if (pmd_none_or_clear_bad(pmd))
+ continue;
+ shrink_pvma_scan_ptes(sc, mm, vma, pmd, addr, next);
+ } while (pmd++, addr = next, addr != end);
+}
+
+static void shrink_pvma_pud_range(struct scan_control* sc, struct mm_struct*
+ mm, struct vm_area_struct* vma, pgd_t* pgd, unsigned long addr,
+ unsigned long end)
+{
+ unsigned long next;
+ pud_t* pud = pud_offset(pgd, addr);
+ do {
+ next = pud_addr_end(addr, end);
+ if (pud_none_or_clear_bad(pud))
+ continue;
+ shrink_pvma_pmd_range(sc, mm, vma, pud, addr, next);
+ } while (pud++, addr = next, addr != end);
+}
+
+static void shrink_pvma_pgd_range(struct scan_control* sc, struct mm_struct*
+ mm, struct vm_area_struct* vma)
+{
+ unsigned long next;
+ unsigned long addr = vma->vm_start;
+ unsigned long end = vma->vm_end;
+ pgd_t* pgd = pgd_offset(mm, addr);
+ do {
+ next = pgd_addr_end(addr, end);
+ if (pgd_none_or_clear_bad(pgd))
+ continue;
+ shrink_pvma_pud_range(sc, mm, vma, pgd, addr, next);
+ } while (pgd++, addr = next, addr != end);
+}
+
+static void shrink_private_vma(struct scan_control* sc)
+{
+ struct vm_area_struct* vma;
+ struct list_head *pos;
+ struct mm_struct *prev, *mm;
+
+ prev = mm = &init_mm;
+ pos = &init_mm.mmlist;
+ atomic_inc(&prev->mm_users);
+ spin_lock(&mmlist_lock);
+ while ((pos = pos->next) != &init_mm.mmlist) {
+ mm = list_entry(pos, struct mm_struct, mmlist);
+ if (!atomic_add_unless(&mm->mm_users, 1, 0))
+ continue;
+ spin_unlock(&mmlist_lock);
+ mmput(prev);
+ prev = mm;
+ start_tlb_tasks(mm);
+ if (down_read_trylock(&mm->mmap_sem)) {
+ for (vma = mm->mmap; vma != NULL; vma = vma->vm_next) {
+ if (!(vma->vm_flags & VM_PURE_PRIVATE))
+ continue;
+ if (vma->vm_flags & VM_LOCKED)
+ continue;
+ shrink_pvma_pgd_range(sc, mm, vma);
+ }
+ up_read(&mm->mmap_sem);
+ }
+ end_tlb_tasks();
+ spin_lock(&mmlist_lock);
+ }
+ spin_unlock(&mmlist_lock);
+ mmput(prev);
+}
+
/*
* For kswapd, balance_pgdat() will work across all this node's zones until
* they are all at pages_high.
@@ -1557,6 +1982,10 @@
sc.may_swap = 1;
sc.nr_mapped = read_page_state(nr_mapped);

+ wakeup_sc = sc;
+ wakeup_sc.pps_cmd = 1;
+ wake_up_interruptible(&kppsd_wait);
+
inc_page_state(pageoutrun);

for (i = 0; i < pgdat->nr_zones; i++) {
@@ -1693,6 +2122,33 @@
return total_reclaimed;
}

+static int kppsd(void* p)
+{
+ struct task_struct *tsk = current;
+ int timeout;
+ DEFINE_WAIT(wait);
+ daemonize("kppsd");
+ tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE;
+ struct scan_control default_sc;
+ default_sc.gfp_mask = GFP_KERNEL;
+ default_sc.may_writepage = 1;
+ default_sc.may_swap = 1;
+ default_sc.pps_cmd = 0;
+
+ while (1) {
+ try_to_freeze();
+ prepare_to_wait(&kppsd_wait, &wait, TASK_INTERRUPTIBLE);
+ timeout = schedule_timeout(2000);
+ finish_wait(&kppsd_wait, &wait);
+
+ if (timeout)
+ shrink_private_vma(&wakeup_sc);
+ else
+ shrink_private_vma(&default_sc);
+ }
+ return 0;
+}
+
/*
* The background pageout daemon, started as a kernel thread
* from the init process.
@@ -1837,6 +2293,15 @@
}
#endif /* CONFIG_HOTPLUG_CPU */

+static int __init kppsd_init(void)
+{
+ init_waitqueue_head(&kppsd_wait);
+ kernel_thread(kppsd, NULL, CLONE_KERNEL);
+ return 0;
+}
+
+module_init(kppsd_init)
+
static int __init kswapd_init(void)
{
pg_data_t *pgdat;

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