| Message ID | b2ea5b52-311d-4c6c-a59d-9982b8723738@vivo.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm: attempt to batch free swap entries for zap_pte_range() | expand |
Next time, please use "> " and ">> " etc to reply to emails. On Tue, Aug 6, 2024 at 3:23 PM zhiguojiang <justinjiang@vivo.com> wrote: > > From: Barry Song <v-songbaohua@oppo.com> > > Zhiguo reported that swap release could be a serious bottleneck > during process exits[1]. With mTHP, we have the opportunity to > batch free swaps. > Thanks to the work of Chris and Kairui[2], I was able to achieve > this optimization with minimal code changes by building on their > efforts. > If swap_count is 1, which is likely true as most anon memory are > private, we can free all contiguous swap slots all together. > > Ran the below test program for measuring the bandwidth of munmap > using zRAM and 64KiB mTHP: > > #include <sys/mman.h> > #include <sys/time.h> > #include <stdlib.h> > > unsigned long long tv_to_ms(struct timeval tv) > { > return tv.tv_sec * 1000 + tv.tv_usec / 1000; > } > > main() > { > struct timeval tv_b, tv_e; > int i; > #define SIZE 1024*1024*1024 > void *p = mmap(NULL, SIZE, PROT_READ | PROT_WRITE, > MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); > if (!p) { > perror("fail to get memory"); > exit(-1); > } > > madvise(p, SIZE, MADV_HUGEPAGE); > memset(p, 0x11, SIZE); /* write to get mem */ > > madvise(p, SIZE, MADV_PAGEOUT); > > gettimeofday(&tv_b, NULL); > munmap(p, SIZE); > gettimeofday(&tv_e, NULL); > > printf("munmap in bandwidth: %ld bytes/ms\n", > SIZE/(tv_to_ms(tv_e) - tv_to_ms(tv_b))); > } > > The result is as below (munmap bandwidth): > mm-unstable mm-unstable-with-patch > round1 21053761 63161283 > round2 21053761 63161283 > round3 21053761 63161283 > round4 20648881 67108864 > round5 20648881 67108864 > > munmap bandwidth becomes 3X faster. > > [1] https://lore.kernel.org/linux-mm/20240731133318.527-1-justinjiang@vivo.com/ > [2] https://lore.kernel.org/linux-mm/20240730-swap-allocator-v5-0-cb9c148b9297@kernel.org/ > > Cc: Kairui Song <kasong@tencent.com> > Cc: Chris Li <chrisl@kernel.org> > Cc: "Huang, Ying" <ying.huang@intel.com> > Cc: Hugh Dickins <hughd@google.com> > Cc: Kalesh Singh <kaleshsingh@google.com> > Cc: Ryan Roberts <ryan.roberts@arm.com> > Cc: David Hildenbrand <david@redhat.com> > Signed-off-by: Barry Song <v-songbaohua@oppo.com> > --- > mm/swapfile.c | 61 +++++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 61 insertions(+) > > diff --git a/mm/swapfile.c b/mm/swapfile.c > index ea023fc25d08..ed872a186e81 100644 > --- a/mm/swapfile.c > +++ b/mm/swapfile.c > @@ -156,6 +156,25 @@ static bool swap_is_has_cache(struct swap_info_struct *si, > return true; > } > > +static bool swap_is_last_map(struct swap_info_struct *si, > + unsigned long offset, int nr_pages, > + bool *has_cache) > +{ > + unsigned char *map = si->swap_map + offset; > + unsigned char *map_end = map + nr_pages; > + bool cached = false; > + > + do { > + if ((*map & ~SWAP_HAS_CACHE) != 1) > + return false; > + if (*map & SWAP_HAS_CACHE) > + cached = true; > + } while (++map < map_end); > + > + *has_cache = cached; > + return true; > +} > + > /* > * returns number of pages in the folio that backs the swap entry. If positive, > * the folio was reclaimed. If negative, the folio was not reclaimed. If 0, no > @@ -1469,6 +1488,39 @@ static unsigned char __swap_entry_free(struct swap_info_struct *p, > return usage; > } > > +static bool try_batch_swap_entries_free(struct swap_info_struct *p, > + swp_entry_t entry, int nr, bool *any_only_cache) > +{ > + unsigned long offset = swp_offset(entry); > + struct swap_cluster_info *ci; > + bool has_cache = false; > + bool can_batch; > + int i; > + > + /* cross into another cluster */ > + if (nr > SWAPFILE_CLUSTER - offset % SWAPFILE_CLUSTER) > + return false; > My understand of mTHP swap entries alloced by by cluster_alloc_swap() > is that they belong to the same cluster in the same swapinfo , so > theoretically it will not appear for > (nr > SWAPFILE_CLUSTER - offset % SWAPFILE_CLUSTER)? > Can you help confirm? zap_pte_range() has no concept of folios (mTHP) as folios could have gone. you could have the case: folio1: last 16 slots of cluster1 folio2: first 16 slots of cluster2. folio1 and folio2 are within the same PMD and virtually contiguous before they are unmapped. when both folio1 and folio2 have gone, zap_pte_range() 's nr = swap_pte_batch(pte, max_nr, ptent); nr will be 32. "mTHP swap entries alloced by by cluster_alloc_swap() belong to the same cluster" is correct, but when you zap_pte_range(), your mTHPs could have gone. > > + ci = lock_cluster_or_swap_info(p, offset); > + can_batch = swap_is_last_map(p, offset, nr, &has_cache); > + if (can_batch) { > + for (i = 0; i < nr; i++) > + WRITE_ONCE(p->swap_map[offset + i], SWAP_HAS_CACHE); > + } > + unlock_cluster_or_swap_info(p, ci); > + > + /* all swap_maps have count==1 and have no swapcache */ > + if (!can_batch) > + goto out; > + if (!has_cache) { > + spin_lock(&p->lock); > + swap_entry_range_free(p, entry, nr); > + spin_unlock(&p->lock); > + } > + *any_only_cache = has_cache; > +out: > + return can_batch; > +} > + > /* > * Drop the last HAS_CACHE flag of swap entries, caller have to > * ensure all entries belong to the same cgroup. > @@ -1797,6 +1849,7 @@ void free_swap_and_cache_nr(swp_entry_t entry, int nr) > bool any_only_cache = false; > unsigned long offset; > unsigned char count; > + bool batched; > > if (non_swap_entry(entry)) > return; > @@ -1808,6 +1861,13 @@ void free_swap_and_cache_nr(swp_entry_t entry, int nr) > if (WARN_ON(end_offset > si->max)) > goto out; > > + if (nr > 1 && swap_count(data_race(si->swap_map[start_offset]) == 1)) { > + batched = try_batch_swap_entries_free(si, entry, nr, > + &any_only_cache); > + if (batched) > + goto reclaim; > + } > The mTHP swap entries are batch freed as a whole directly by skipping > percpu swp_slots caches, instead of freeing every swap entry separately, > which can accelerate the mTHP swap entries release. I think it is > valuable. yes. I have seen 3X performance improvement. > > + > /* > * First free all entries in the range. > */ > @@ -1821,6 +1881,7 @@ void free_swap_and_cache_nr(swp_entry_t entry, int nr) > } > } > > +reclaim: > /* > * Short-circuit the below loop if none of the entries had their > * reference drop to zero. > -- > 2.34.1 > > Thanks > Zhiguo > > > Thanks Barry
diff --git a/mm/swapfile.c b/mm/swapfile.c index ea023fc25d08..ed872a186e81 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -156,6 +156,25 @@ static bool swap_is_has_cache(struct swap_info_struct *si, return true; } +static bool swap_is_last_map(struct swap_info_struct *si, + unsigned long offset, int nr_pages, + bool *has_cache) +{ + unsigned char *map = si->swap_map + offset; + unsigned char *map_end = map + nr_pages; + bool cached = false; + + do { + if ((*map & ~SWAP_HAS_CACHE) != 1) + return false; + if (*map & SWAP_HAS_CACHE) + cached = true; + } while (++map < map_end); + + *has_cache = cached; + return true; +} + /* * returns number of pages in the folio that backs the swap entry. If positive, * the folio was reclaimed. If negative, the folio was not reclaimed. If 0, no @@ -1469,6 +1488,39 @@ static unsigned char __swap_entry_free(struct swap_info_struct *p, return usage; } +static bool try_batch_swap_entries_free(struct swap_info_struct *p, + swp_entry_t entry, int nr, bool *any_only_cache) +{ + unsigned long offset = swp_offset(entry); + struct swap_cluster_info *ci; + bool has_cache = false; + bool can_batch; + int i; + + /* cross into another cluster */ + if (nr > SWAPFILE_CLUSTER - offset % SWAPFILE_CLUSTER) + return false; My understand of mTHP swap entries alloced by by cluster_alloc_swap() is that they belong to the same cluster in the same swapinfo , so theoretically it will not appear for (nr > SWAPFILE_CLUSTER - offset % SWAPFILE_CLUSTER)? Can you help confirm? + ci = lock_cluster_or_swap_info(p, offset); + can_batch = swap_is_last_map(p, offset, nr, &has_cache); + if (can_batch) { + for (i = 0; i < nr; i++) + WRITE_ONCE(p->swap_map[offset + i], SWAP_HAS_CACHE); + } + unlock_cluster_or_swap_info(p, ci); + + /* all swap_maps have count==1 and have no swapcache */ + if (!can_batch) + goto out; + if (!has_cache) { + spin_lock(&p->lock); + swap_entry_range_free(p, entry, nr); + spin_unlock(&p->lock); + } + *any_only_cache = has_cache; +out: