On 2025/6/25 16:45, Chao Yu wrote:
>
> On 6/25/25 14:49, Jianan Huang wrote:
>> When fewer pages are read, nr_pages may be smaller than nr_cpages. Due
>> to the nr_vecs limit, the compressed pages will be split into multiple
>> bios and then merged at the block level. In this case, nr_cpages should
>> be used to pre-allocate bvecs.
>> To handle this case, align max_nr_pages to cluster_size, which should be
>> enough for all compressed pages.
>>
>> Signed-off-by: Jianan Huang <huangjia...@xiaomi.com>
>> Signed-off-by: Sheng Yong <shengyo...@xiaomi.com>
>> ---
>> Changes since v2:
>> - Initialize index only for compressed files.
>> Changes since v1:
>> - Use aligned nr_pages instead of nr_cpages to pre-allocate bvecs.
>>
>> fs/f2fs/data.c | 12 ++++++++++--
>> 1 file changed, 10 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
>> index 31e892842625..d071d9f6a811 100644
>> --- a/fs/f2fs/data.c
>> +++ b/fs/f2fs/data.c
>> @@ -2303,7 +2303,7 @@ int f2fs_read_multi_pages(struct compress_ctx *cc,
>> struct bio **bio_ret,
>> }
>>
>> if (!bio) {
>> - bio = f2fs_grab_read_bio(inode, blkaddr, nr_pages,
>> + bio = f2fs_grab_read_bio(inode, blkaddr, nr_pages - i,
>
> Jianan,
>
> Another case:
>
> read page #0,1,2,3 from block #1000,1001,1002, cluster_size=4.
>
> nr_pages=4
> max_nr_pages=round_up(0+4,4)-round_down(0,4)=4
>
> f2fs_mpage_readpages() calls f2fs_read_multi_pages() when nr_pages=1, at
> that time, max_nr_pages equals to 1 as well.
>
> f2fs_grab_read_bio(..., 1 - 0,...) allocate bio w/ 1 vec capacity, however,
> we need at least 3 vecs to merge all cpages, right?
>
Hi, chao,
If we don't align nr_pages, then when entering f2fs_read_multi_pages,
we have nr_pages pages left, which belong to other clusters.
If this is the last page, we can simply pass nr_pages = 0.
When allocating bio, we need:
1. The cpages remaining in the current cluster, which should be
(nr_capges - i).
2. The maximum cpages remaining in other clusters, which should be
max(nr_pages, cc->nr_cpages).
So (nr_capges - i) + max(nr_pages, nr_cpages), should be enough for all
vecs?
Thanks,
> Thanks,
>
>> f2fs_ra_op_flags(rac),
>> folio->index, for_write);
>> if (IS_ERR(bio)) {
>> @@ -2376,6 +2376,14 @@ static int f2fs_mpage_readpages(struct inode *inode,
>> unsigned max_nr_pages = nr_pages;
>> int ret = 0;
>>
>> +#ifdef CONFIG_F2FS_FS_COMPRESSION
>> + if (f2fs_compressed_file(inode)) {
>> + index = rac ? readahead_index(rac) : folio->index;
>> + max_nr_pages = round_up(index + nr_pages, cc.cluster_size) -
>> + round_down(index, cc.cluster_size);
>> + }
>> +#endif
>> +
>> map.m_pblk = 0;
>> map.m_lblk = 0;
>> map.m_len = 0;
>> @@ -2385,7 +2393,7 @@ static int f2fs_mpage_readpages(struct inode *inode,
>> map.m_seg_type = NO_CHECK_TYPE;
>> map.m_may_create = false;
>>
>> - for (; nr_pages; nr_pages--) {
>> + for (; nr_pages; nr_pages--, max_nr_pages--) {
>> if (rac) {
>> folio = readahead_folio(rac);
>> prefetchw(&folio->flags);
>
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