Re: [RFC PATCH v5 3/4] erofs: apply the page cache share feature

[Gao Xiang]

On 2025/1/5 23:12, Hongzhen Luo wrote:

...

diff --git a/fs/erofs/data.c b/fs/erofs/data.c
index 0cd6b5c4df98..fb08acbeaab6 100644
--- a/fs/erofs/data.c
+++ b/fs/erofs/data.c
@@ -5,6 +5,7 @@
   * Copyright (C) 2021, Alibaba Cloud
   */
  #include "internal.h"
+#include "pagecache_share.h"
  #include <linux/sched/mm.h>
  #include <trace/events/erofs.h>

@@ -370,12 +371,21 @@ int erofs_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,

   */
  static int erofs_read_folio(struct file *file, struct folio *folio)
  {
-       return iomap_read_folio(folio, &erofs_iomap_ops);
+       int ret, pcshr;
+
+       pcshr = erofs_pcshr_read_begin(file, folio);
+       ret = iomap_read_folio(folio, &erofs_iomap_ops);
+       erofs_pcshr_read_end(file, folio, pcshr);
+       return ret;
  }

static void erofs_readahead(struct readahead_control *rac)

  {
-       return iomap_readahead(rac, &erofs_iomap_ops);
+       int pcshr;
+
+       pcshr = erofs_pcshr_readahead_begin(rac);
+       iomap_readahead(rac, &erofs_iomap_ops);
+       erofs_pcshr_readahead_end(rac, pcshr);
  }

static sector_t erofs_bmap(struct address_space *mapping, sector_t block)

diff --git a/fs/erofs/inode.c b/fs/erofs/inode.c
index d4b89407822a..0b070f4b46b8 100644
--- a/fs/erofs/inode.c
+++ b/fs/erofs/inode.c
@@ -5,6 +5,7 @@
   * Copyright (C) 2021, Alibaba Cloud
   */
  #include "xattr.h"
+#include "pagecache_share.h"
  #include <trace/events/erofs.h>

static int erofs_fill_symlink(struct inode *inode, void *kaddr,

@@ -212,7 +213,9 @@ static int erofs_fill_inode(struct inode *inode)
        switch (inode->i_mode & S_IFMT) {
        case S_IFREG:
                inode->i_op = &erofs_generic_iops;
-               if (erofs_inode_is_data_compressed(vi->datalayout))
+               if (erofs_pcshr_fill_inode(inode) == 0)
+                       inode->i_fop = &erofs_pcshr_fops;
+               else if (erofs_inode_is_data_compressed(vi->datalayout))
                        inode->i_fop = &generic_ro_fops;
                else
                        inode->i_fop = &erofs_file_fops;
diff --git a/fs/erofs/pagecache_share.c b/fs/erofs/pagecache_share.c
index 703fd17c002c..22172b5e21c7 100644
--- a/fs/erofs/pagecache_share.c
+++ b/fs/erofs/pagecache_share.c
@@ -22,6 +22,7 @@ struct erofs_pcshr_counter {

struct erofs_pcshr_private {

        char fprt[PCSHR_FPRT_MAXLEN];
+       struct mutex mutex;
  };

static struct erofs_pcshr_counter mnt_counter = {

@@ -84,6 +85,7 @@ static int erofs_fprt_set(struct inode *inode, void *data)
        if (!ano_private)
                return -ENOMEM;
        memcpy(ano_private, data, sizeof(size_t) + *(size_t *)data);
+       mutex_init(&ano_private->mutex);
        inode->i_private = ano_private;
        return 0;
  }
@@ -226,3 +228,64 @@ const struct file_operations erofs_pcshr_fops = {
        .get_unmapped_area = thp_get_unmapped_area,
        .splice_read    = filemap_splice_read,
  };
+
+int erofs_pcshr_read_begin(struct file *file, struct folio *folio)
+{
+       struct erofs_inode *vi;
+       struct erofs_pcshr_private *ano_private;
+
+       if (!(file && file->private_data))
+               return 0;
+
+       vi = file->private_data;
+       if (vi->ano_inode != file_inode(file))
+               return 0;
+
+       ano_private = vi->ano_inode->i_private;
+       mutex_lock(&ano_private->mutex);
+       folio->mapping->host = &vi->vfs_inode;

you shouldn't change `folio->mapping->host` directly.

+       return 1;
+}
+
+void erofs_pcshr_read_end(struct file *file, struct folio *folio, int pcshr)
+{
+       struct erofs_pcshr_private *ano_private;
+
+       if (pcshr == 0)
+               return;
+
+       ano_private = file_inode(file)->i_private;
+       folio->mapping->host = file_inode(file);

you shouldn't change `folio->mapping->host` directly
and then switch back.  It's too hacky.

+       mutex_unlock(&ano_private->mutex);
+}
+
+int erofs_pcshr_readahead_begin(struct readahead_control *rac)
+{
+       struct erofs_inode *vi;
+       struct file *file = rac->file;
+       struct erofs_pcshr_private *ano_private;
+
+       if (!(file && file->private_data))
+               return 0;
+
+       vi = file->private_data;
+       if (vi->ano_inode != file_inode(file))
+               return 0;
+
+       ano_private = file_inode(file)->i_private;
+       mutex_lock(&ano_private->mutex);
+       rac->mapping->host = &vi->vfs_inode;

Same here.

Thanks,
Gao Xiang