UNMAP_MAPPING_RANGE(9) Memory Management in Linux UNMAP_MAPPING_RANGE(9)NAME
unmap_mapping_range - unmap the portion of all mmaps in the specified address_space corresponding to the specified page range in the
underlying file.
SYNOPSIS
void unmap_mapping_range(struct address_space * mapping, loff_t const holebegin, loff_t const holelen, int even_cows);
ARGUMENTS
mapping
the address space containing mmaps to be unmapped.
holebegin
byte in first page to unmap, relative to the start of the underlying file. This will be rounded down to a PAGE_SIZE boundary. Note that
this is different from truncate_pagecache, which must keep the partial page. In contrast, we must get rid of partial pages.
holelen
size of prospective hole in bytes. This will be rounded up to a PAGE_SIZE boundary. A holelen of zero truncates to the end of the file.
even_cows
1 when truncating a file, unmap even private COWed pages; but 0 when invalidating pagecache, don't throw away private data.
COPYRIGHT Kernel Hackers Manual 3.10 June 2014 UNMAP_MAPPING_RANGE(9)
Check Out this Related Man Page
MPAGE_READPAGES(9) The Linux VFS MPAGE_READPAGES(9)NAME
mpage_readpages - populate an address space with some pages & start reads against them
SYNOPSIS
int mpage_readpages(struct address_space * mapping, struct list_head * pages, unsigned nr_pages, get_block_t get_block);
ARGUMENTS
mapping
the address_space
pages
The address of a list_head which contains the target pages. These pages have their ->index populated and are otherwise uninitialised.
The page at pages->prev has the lowest file offset, and reads should be issued in pages->prev to pages->next order.
nr_pages
The number of pages at *pages
get_block
The filesystem's block mapper function.
DESCRIPTION
This function walks the pages and the blocks within each page, building and emitting large BIOs.
If anything unusual happens, such as:
- encountering a page which has buffers - encountering a page which has a non-hole after a hole - encountering a page with non-contiguous
blocks
then this code just gives up and calls the buffer_head-based read function. It does handle a page which has holes at the end - that is a
common case: the end-of-file on blocksize < PAGE_CACHE_SIZE setups.
BH_BOUNDARY EXPLANATION
There is a problem. The mpage read code assembles several pages, gets all their disk mappings, and then submits them all. That's fine, but
obtaining the disk mappings may require I/O. Reads of indirect blocks, for example.
So an mpage read of the first 16 blocks of an ext2 file will cause I/O to be
SUBMITTED IN THE FOLLOWING ORDER
12 0 1 2 3 4 5 6 7 8 9 10 11 13 14 15 16
because the indirect block has to be read to get the mappings of blocks 13,14,15,16. Obviously, this impacts performance.
So what we do it to allow the filesystem's get_block function to set BH_Boundary when it maps block 11. BH_Boundary says: mapping of the
block after this one will require I/O against a block which is probably close to this one. So you should push what I/O you have currently
accumulated.
This all causes the disk requests to be issued in the correct order.
COPYRIGHT Kernel Hackers Manual 3.10 June 2014 MPAGE_READPAGES(9)
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