TRUNCATE_PAGECACHE_R(9) Memory Management in Linux TRUNCATE_PAGECACHE_R(9)NAME
truncate_pagecache_range - unmap and remove pagecache that is hole-punched
void truncate_pagecache_range(struct inode * inode, loff_t lstart, loff_t lend);
offset of beginning of hole
offset of last byte of hole
This function should typically be called before the filesystem releases resources associated with the freed range (eg. deallocates blocks).
This way, pagecache will always stay logically coherent with on-disk format, and the filesystem would not have to deal with situations such
as writepage being called for a page that has already had its underlying blocks deallocated.
COPYRIGHT Kernel Hackers Manual 3.10 June 2014 TRUNCATE_PAGECACHE_R(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
int mpage_readpages(struct address_space * mapping, struct list_head * pages, unsigned nr_pages, get_block_t get_block);
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.
The number of pages at *pages
The filesystem's block mapper function.
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
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.
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
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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