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charset="us-ascii" X-Rspamd-Server: rspam06 X-Stat-Signature: cbaikhafy3em678hmajhmsqwo3hf3zub X-Rspam-User: X-Rspamd-Queue-Id: CDE1C40017 X-HE-Tag: 1718223234-433584 X-HE-Meta: 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 VTFaIYhq 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Jun 12, 2024 at 01:43:35PM +0100, Usama Arif wrote: [..] Hi Usama, A few more comments/questions, sorry for not looking closely earlier. > diff --git a/mm/swapfile.c b/mm/swapfile.c > index f1e559e216bd..48d8dca0b94b 100644 > --- a/mm/swapfile.c > +++ b/mm/swapfile.c > @@ -453,6 +453,8 @@ static unsigned int cluster_list_del_first(struct swap_cluster_list *list, > static void swap_cluster_schedule_discard(struct swap_info_struct *si, > unsigned int idx) > { > + unsigned int i; > + > /* > * If scan_swap_map_slots() can't find a free cluster, it will check > * si->swap_map directly. To make sure the discarding cluster isn't > @@ -461,6 +463,13 @@ static void swap_cluster_schedule_discard(struct swap_info_struct *si, > */ > memset(si->swap_map + idx * SWAPFILE_CLUSTER, > SWAP_MAP_BAD, SWAPFILE_CLUSTER); > + /* > + * zeromap can see updates from concurrent swap_writepage() and swap_read_folio() > + * call on other slots, hence use atomic clear_bit for zeromap instead of the > + * non-atomic bitmap_clear. > + */ I don't think this is accurate. swap_read_folio() does not update the zeromap. I think the need for an atomic operation here is because we may be updating adjacent bits simulatenously, so we may cause lost updates otherwise (i.e. corrupting adjacent bits). > + for (i = 0; i < SWAPFILE_CLUSTER; i++) > + clear_bit(idx * SWAPFILE_CLUSTER + i, si->zeromap); Could you explain why we need to clear the zeromap here? swap_cluster_schedule_discard() is called from: - swap_free_cluster() -> free_cluster() This is already covered below. - swap_entry_free() -> dec_cluster_info_page() -> free_cluster() Each entry in the cluster should have its zeromap bit cleared in swap_entry_free() before the entire cluster is free and we call free_cluster(). Am I missing something? > > cluster_list_add_tail(&si->discard_clusters, si->cluster_info, idx); > > @@ -482,7 +491,7 @@ static void __free_cluster(struct swap_info_struct *si, unsigned long idx) > static void swap_do_scheduled_discard(struct swap_info_struct *si) > { > struct swap_cluster_info *info, *ci; > - unsigned int idx; > + unsigned int idx, i; > > info = si->cluster_info; > > @@ -498,6 +507,8 @@ static void swap_do_scheduled_discard(struct swap_info_struct *si) > __free_cluster(si, idx); > memset(si->swap_map + idx * SWAPFILE_CLUSTER, > 0, SWAPFILE_CLUSTER); > + for (i = 0; i < SWAPFILE_CLUSTER; i++) > + clear_bit(idx * SWAPFILE_CLUSTER + i, si->zeromap); Same here. I didn't look into the specific code paths, but shouldn't the cluster be unused (and hence its zeromap bits already cleared?). > unlock_cluster(ci); > } > } > @@ -1059,9 +1070,12 @@ static void swap_free_cluster(struct swap_info_struct *si, unsigned long idx) > { > unsigned long offset = idx * SWAPFILE_CLUSTER; > struct swap_cluster_info *ci; > + unsigned int i; > > ci = lock_cluster(si, offset); > memset(si->swap_map + offset, 0, SWAPFILE_CLUSTER); > + for (i = 0; i < SWAPFILE_CLUSTER; i++) > + clear_bit(offset + i, si->zeromap); > cluster_set_count_flag(ci, 0, 0); > free_cluster(si, idx); > unlock_cluster(ci); > @@ -1336,6 +1350,7 @@ static void swap_entry_free(struct swap_info_struct *p, swp_entry_t entry) > count = p->swap_map[offset]; > VM_BUG_ON(count != SWAP_HAS_CACHE); > p->swap_map[offset] = 0; > + clear_bit(offset, p->zeromap); I think instead of clearing the zeromap in swap_free_cluster() and here separately, we can just do it in swap_range_free(). I suspect this may be the only place we really need to clear the zero in the swapfile code. > dec_cluster_info_page(p, p->cluster_info, offset); > unlock_cluster(ci); > > @@ -2597,6 +2612,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile) > free_percpu(p->cluster_next_cpu); > p->cluster_next_cpu = NULL; > vfree(swap_map); > + bitmap_free(p->zeromap); > kvfree(cluster_info); > /* Destroy swap account information */ > swap_cgroup_swapoff(p->type); > @@ -3123,6 +3139,12 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) > goto bad_swap_unlock_inode; > } > > + p->zeromap = bitmap_zalloc(maxpages, GFP_KERNEL); > + if (!p->zeromap) { > + error = -ENOMEM; > + goto bad_swap_unlock_inode; > + } > + > if (p->bdev && bdev_stable_writes(p->bdev)) > p->flags |= SWP_STABLE_WRITES; > > -- > 2.43.0 >