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Date: Mon, 28 Nov 2022 21:54:41 +0800
From: Jia Zhu <zhujia.zj@...edance.com>
To: Jingbo Xu <jefflexu@...ux.alibaba.com>, xiang@...nel.org,
chao@...nel.org, linux-erofs@...ts.ozlabs.org
Cc: linux-kernel@...r.kernel.org
Subject: Re: [Phishing Risk] [External] [PATCH v2 1/2] erofs: support large
folios for fscache mode
在 2022/11/28 10:50, Jingbo Xu 写道:
> When large folios supported, one folio can be split into several slices,
> each of which may be mapped to META/UNMAPPED/MAPPED, and the folio can
> be unlocked as a whole only when all slices have completed.
>
> Thus always allocate erofs_fscache_request for each .read_folio() or
> .readahead(). In this case, only when all slices of the folio or folio
> range have completed, the request will be marked as completed and the
> folio or folio range will be unlocked then.
>
> Signed-off-by: Jingbo Xu <jefflexu@...ux.alibaba.com>
Reviewed-by: Jia Zhu <zhujia.zj@...edance.com>
Thanks.
> ---
> fs/erofs/fscache.c | 116 +++++++++++++++++++--------------------------
> 1 file changed, 48 insertions(+), 68 deletions(-)
>
> diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
> index 3cfe1af7a46e..0643b205c7eb 100644
> --- a/fs/erofs/fscache.c
> +++ b/fs/erofs/fscache.c
> @@ -167,32 +167,18 @@ static int erofs_fscache_meta_read_folio(struct file *data, struct folio *folio)
> return ret;
> }
>
> -/*
> - * Read into page cache in the range described by (@pos, @len).
> - *
> - * On return, if the output @unlock is true, the caller is responsible for page
> - * unlocking; otherwise the callee will take this responsibility through request
> - * completion.
> - *
> - * The return value is the number of bytes successfully handled, or negative
> - * error code on failure. The only exception is that, the length of the range
> - * instead of the error code is returned on failure after request is allocated,
> - * so that .readahead() could advance rac accordingly.
> - */
> -static int erofs_fscache_data_read(struct address_space *mapping,
> - loff_t pos, size_t len, bool *unlock)
> +static int erofs_fscache_data_read_slice(struct erofs_fscache_request *req)
> {
> + struct address_space *mapping = req->mapping;
> struct inode *inode = mapping->host;
> struct super_block *sb = inode->i_sb;
> - struct erofs_fscache_request *req;
> + loff_t pos = req->start + req->submitted;
> struct erofs_map_blocks map;
> struct erofs_map_dev mdev;
> struct iov_iter iter;
> size_t count;
> int ret;
>
> - *unlock = true;
> -
> map.m_la = pos;
> ret = erofs_map_blocks(inode, &map, EROFS_GET_BLOCKS_RAW);
> if (ret)
> @@ -201,36 +187,37 @@ static int erofs_fscache_data_read(struct address_space *mapping,
> if (map.m_flags & EROFS_MAP_META) {
> struct erofs_buf buf = __EROFS_BUF_INITIALIZER;
> erofs_blk_t blknr;
> - size_t offset, size;
> + size_t offset;
> void *src;
>
> /* For tail packing layout, the offset may be non-zero. */
> offset = erofs_blkoff(map.m_pa);
> blknr = erofs_blknr(map.m_pa);
> - size = map.m_llen;
> + count = map.m_llen;
>
> src = erofs_read_metabuf(&buf, sb, blknr, EROFS_KMAP);
> if (IS_ERR(src))
> return PTR_ERR(src);
>
> - iov_iter_xarray(&iter, READ, &mapping->i_pages, pos, PAGE_SIZE);
> - if (copy_to_iter(src + offset, size, &iter) != size) {
> + iov_iter_xarray(&iter, READ, &mapping->i_pages, pos, count);
> + if (copy_to_iter(src + offset, count, &iter) != count) {
> erofs_put_metabuf(&buf);
> return -EFAULT;
> }
> - iov_iter_zero(PAGE_SIZE - size, &iter);
> erofs_put_metabuf(&buf);
> - return PAGE_SIZE;
> + req->submitted += count;
> + return 0;
> }
>
> + count = req->len - req->submitted;
> if (!(map.m_flags & EROFS_MAP_MAPPED)) {
> - count = len;
> iov_iter_xarray(&iter, READ, &mapping->i_pages, pos, count);
> iov_iter_zero(count, &iter);
> - return count;
> + req->submitted += count;
> + return 0;
> }
>
> - count = min_t(size_t, map.m_llen - (pos - map.m_la), len);
> + count = min_t(size_t, map.m_llen - (pos - map.m_la), count);
> DBG_BUGON(!count || count % PAGE_SIZE);
>
> mdev = (struct erofs_map_dev) {
> @@ -241,68 +228,61 @@ static int erofs_fscache_data_read(struct address_space *mapping,
> if (ret)
> return ret;
>
> - req = erofs_fscache_req_alloc(mapping, pos, count);
> - if (IS_ERR(req))
> - return PTR_ERR(req);
> -
> - *unlock = false;
> - ret = erofs_fscache_read_folios_async(mdev.m_fscache->cookie,
> + return erofs_fscache_read_folios_async(mdev.m_fscache->cookie,
> req, mdev.m_pa + (pos - map.m_la), count);
> - if (ret)
> - req->error = ret;
> +}
>
> - erofs_fscache_req_put(req);
> - return count;
> +/*
> + * Read into page cache in the range described by (req->start, req->len).
> + */
> +static int erofs_fscache_data_read(struct erofs_fscache_request *req)
> +{
> + int ret;
> +
> + do {
> + ret = erofs_fscache_data_read_slice(req);
> + if (ret)
> + req->error = ret;
> + } while (!ret && req->submitted < req->len);
> +
> + return ret;
> }
>
> static int erofs_fscache_read_folio(struct file *file, struct folio *folio)
> {
> - bool unlock;
> + struct erofs_fscache_request *req;
> int ret;
>
> - DBG_BUGON(folio_size(folio) != EROFS_BLKSIZ);
> -
> - ret = erofs_fscache_data_read(folio_mapping(folio), folio_pos(folio),
> - folio_size(folio), &unlock);
> - if (unlock) {
> - if (ret > 0)
> - folio_mark_uptodate(folio);
> + req = erofs_fscache_req_alloc(folio_mapping(folio),
> + folio_pos(folio), folio_size(folio));
> + if (IS_ERR(req)) {
> folio_unlock(folio);
> + return PTR_ERR(req);
> }
> - return ret < 0 ? ret : 0;
> +
> + ret = erofs_fscache_data_read(req);
> + erofs_fscache_req_put(req);
> + return ret;
> }
>
> static void erofs_fscache_readahead(struct readahead_control *rac)
> {
> - struct folio *folio;
> - size_t len, done = 0;
> - loff_t start, pos;
> - bool unlock;
> - int ret, size;
> + struct erofs_fscache_request *req;
>
> if (!readahead_count(rac))
> return;
>
> - start = readahead_pos(rac);
> - len = readahead_length(rac);
> + req = erofs_fscache_req_alloc(rac->mapping,
> + readahead_pos(rac), readahead_length(rac));
> + if (IS_ERR(req))
> + return;
>
> - do {
> - pos = start + done;
> - ret = erofs_fscache_data_read(rac->mapping, pos,
> - len - done, &unlock);
> - if (ret <= 0)
> - return;
> + /* The request completion will drop refs on the folios. */
> + while (readahead_folio(rac))
> + ;
>
> - size = ret;
> - while (size) {
> - folio = readahead_folio(rac);
> - size -= folio_size(folio);
> - if (unlock) {
> - folio_mark_uptodate(folio);
> - folio_unlock(folio);
> - }
> - }
> - } while ((done += ret) < len);
> + erofs_fscache_data_read(req);
> + erofs_fscache_req_put(req);
> }
>
> static const struct address_space_operations erofs_fscache_meta_aops = {
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