On 01/07/2024 18:37, Usama Arif wrote: > > On 01/07/2024 18:01, Usama Arif wrote: >> >> On 28/06/2024 18:30, Usama Arif wrote: >>> >>> On 27/06/2024 19:18, Johannes Weiner wrote: >>>> Hi Usama, >>>> >>>> On Thu, Jun 27, 2024 at 11:55:29AM +0100, Usama Arif wrote: >>>>> Approximately 10-20% of pages to be swapped out are zero pages [1]. >>>>> Rather than reading/writing these pages to flash resulting >>>>> in increased I/O and flash wear, a bitmap can be used to mark these >>>>> pages as zero at write time, and the pages can be filled at >>>>> read time if the bit corresponding to the page is set. >>>>> With this patch, NVMe writes in Meta server fleet decreased >>>>> by almost 10% with conventional swap setup (zswap disabled). >>>>> >>>>> [1] https://lore.kernel.org/all/20171018104832epcms5p1b2232e2236258de3d03d1344dde9fce0@epcms5p1/ >>>>> >>>>> Signed-off-by: Usama Arif <usamaarif642@xxxxxxxxx> >>>>> Reviewed-by: Chengming Zhou <chengming.zhou@xxxxxxxxx> >>>>> Reviewed-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx> >>>>> Reviewed-by: Nhat Pham <nphamcs@xxxxxxxxx> >>>>> Cc: David Hildenbrand <david@xxxxxxxxxx> >>>>> Cc: "Huang, Ying" <ying.huang@xxxxxxxxx> >>>>> Cc: Hugh Dickins <hughd@xxxxxxxxxx> >>>>> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> >>>>> Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> >>>>> Cc: Shakeel Butt <shakeel.butt@xxxxxxxxx> >>>>> Cc: Usama Arif <usamaarif642@xxxxxxxxx> >>>>> Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx> >>>>> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> >>>> This looks great to me, and the numbers speak for themselves. A few >>>> minor comments below: >>>> >>>>> --- >>>>> include/linux/swap.h | 1 + >>>>> mm/page_io.c | 113 ++++++++++++++++++++++++++++++++++++++++++- >>>>> mm/swapfile.c | 20 ++++++++ >>>>> 3 files changed, 133 insertions(+), 1 deletion(-) >>>>> >>>>> diff --git a/include/linux/swap.h b/include/linux/swap.h >>>>> index 3df75d62a835..ed03d421febd 100644 >>>>> --- a/include/linux/swap.h >>>>> +++ b/include/linux/swap.h >>>>> @@ -299,6 +299,7 @@ struct swap_info_struct { >>>>> signed char type; /* strange name for an index */ >>>>> unsigned int max; /* extent of the swap_map */ >>>>> unsigned char *swap_map; /* vmalloc'ed array of usage counts */ >>>>> + unsigned long *zeromap; /* vmalloc'ed bitmap to track zero pages */ >>>>> struct swap_cluster_info *cluster_info; /* cluster info. Only for SSD */ >>>>> struct swap_cluster_list free_clusters; /* free clusters list */ >>>>> unsigned int lowest_bit; /* index of first free in swap_map */ >>>>> diff --git a/mm/page_io.c b/mm/page_io.c >>>>> index 6c1c1828bb88..480b8f221d90 100644 >>>>> --- a/mm/page_io.c >>>>> +++ b/mm/page_io.c >>>>> @@ -172,6 +172,88 @@ int generic_swapfile_activate(struct swap_info_struct *sis, >>>>> goto out; >>>>> } >>>> It might be good to have a short comment that gives 1) an overview, >>>> that we're using a bitmap to avoid doing IO for zero-filled pages and >>>> 2) the locking, that the bits are protected by the locked swapcache >>>> folio and atomic updates are used to protect against RMW corruption >>>> due to other zero swap entries seeing concurrent updates. >>> >>> Thanks! have addressed the comments and will include them in next revision. Just a couple of things. >>> >>> Will add the overview in swap_writepage when the check is made if the folio is zero filled and zeromap bits are set, instead of at this point. >>> >>>>> +static bool is_folio_page_zero_filled(struct folio *folio, int i) >>>>> +{ >>>>> + unsigned long *data; >>>>> + unsigned int pos, last_pos = PAGE_SIZE / sizeof(*data) - 1; >>>>> + bool ret = false; >>>>> + >>>>> + data = kmap_local_folio(folio, i * PAGE_SIZE); >>>>> + if (data[last_pos]) >>>>> + goto out; >>>>> +static void folio_zero_fill(struct folio *folio) >>>>> +{ >>>>> + unsigned int i; >>>>> + >>>>> + for (i = 0; i < folio_nr_pages(folio); i++) >>>>> + clear_highpage(folio_page(folio, i)); >>>>> +} >>>> Should this be in highmem.h next to the other folio_zero_* functions? >>> >>> Thanks for pointing to highmem.h. It already has folio_zero_range, which should do the same thing, so I think I can just do folio_zero_range(folio, 0, folio_size(folio)) and this function shouldnt be needed. >> >> >> How about this? Patch 2 to remove zswap code doesn't change. >> >> > My mail client had messed up the spacing in my previous reply, so it might not apply cleanly. Hoping it comes out correct this time > Sorry for the repeated emails, this one should definitely work. Changes from v7 (Johannes): - Give overview and explain how locking works in zeromap in comments - Add comment for why last word is checked first when checking if folio is zero-filled - Merge is_folio_zero_filled and is_folio_page_zero_filled into 1 function. - Use folio_zero_range to fill a folio with zero at readtime. - Put swap_zeromap_folio_clear in an else branch (even if checkpatch gives warning) and add comment to make it explicitly clear that it needs to happen if folio is not zero filled. - add missing kvfree for zeromap incase swapon fails.
