Adil Mujeeb wrote:
Hi list,
I was going through the chapter 15: The Page Cache of "Understanding the
Linux Kernel".
It was written under "The address_space Object" section:
Quite surprisingly, the page cache may happily contain multiple copies
of the same disk data. For instance, the same 4-KB block of data of a
regular file can be accessed in the following ways:
- Reading the file; hence, the data is included in a page owned by the
regular file's inode.
- Reading the block from the device file (disk partition) that hosts the
file; hence, the data is included in a page owned by the master inode of
the block device file.
I did not understand this part. How the duplicate pages will be present
in the Page cache. Anybody could please elaborate it further.
One page will have page->mapping point to the file's
address_space and have page->index set to offset of
this page into the file.
The other page has page->mapping point to the block
device's address_space and have page->index set to
this page's offset into the block device.
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