diff options
author | Linus Torvalds <torvalds@linux-foundation.org> | 2016-04-04 10:50:24 -0700 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2016-04-04 10:50:24 -0700 |
commit | 4a2d057e4fc4f9ebd32351837c14c10a0773b956 (patch) | |
tree | b0ed0187a6839ebed4982fe7589b410222fd4b9a /fs/cramfs/README | |
parent | 9735a22799b9214d17d3c231fe377fc852f042e9 (diff) | |
parent | 1fa64f198b9f8d6ec0f7aec7c18dc94684391140 (diff) |
Merge branch 'PAGE_CACHE_SIZE-removal'
Merge PAGE_CACHE_SIZE removal patches from Kirill Shutemov:
"PAGE_CACHE_{SIZE,SHIFT,MASK,ALIGN} macros were introduced *long* time
ago with promise that one day it will be possible to implement page
cache with bigger chunks than PAGE_SIZE.
This promise never materialized. And unlikely will.
Let's stop pretending that pages in page cache are special. They are
not.
The first patch with most changes has been done with coccinelle. The
second is manual fixups on top.
The third patch removes macros definition"
[ I was planning to apply this just before rc2, but then I spaced out,
so here it is right _after_ rc2 instead.
As Kirill suggested as a possibility, I could have decided to only
merge the first two patches, and leave the old interfaces for
compatibility, but I'd rather get it all done and any out-of-tree
modules and patches can trivially do the converstion while still also
working with older kernels, so there is little reason to try to
maintain the redundant legacy model. - Linus ]
* PAGE_CACHE_SIZE-removal:
mm: drop PAGE_CACHE_* and page_cache_{get,release} definition
mm, fs: remove remaining PAGE_CACHE_* and page_cache_{get,release} usage
mm, fs: get rid of PAGE_CACHE_* and page_cache_{get,release} macros
Diffstat (limited to 'fs/cramfs/README')
-rw-r--r-- | fs/cramfs/README | 26 |
1 files changed, 13 insertions, 13 deletions
diff --git a/fs/cramfs/README b/fs/cramfs/README index 445d1c2d7646..9d4e7ea311f4 100644 --- a/fs/cramfs/README +++ b/fs/cramfs/README @@ -86,26 +86,26 @@ Block Size (Block size in cramfs refers to the size of input data that is compressed at a time. It's intended to be somewhere around -PAGE_CACHE_SIZE for cramfs_readpage's convenience.) +PAGE_SIZE for cramfs_readpage's convenience.) The superblock ought to indicate the block size that the fs was written for, since comments in <linux/pagemap.h> indicate that -PAGE_CACHE_SIZE may grow in future (if I interpret the comment +PAGE_SIZE may grow in future (if I interpret the comment correctly). -Currently, mkcramfs #define's PAGE_CACHE_SIZE as 4096 and uses that -for blksize, whereas Linux-2.3.39 uses its PAGE_CACHE_SIZE, which in +Currently, mkcramfs #define's PAGE_SIZE as 4096 and uses that +for blksize, whereas Linux-2.3.39 uses its PAGE_SIZE, which in turn is defined as PAGE_SIZE (which can be as large as 32KB on arm). This discrepancy is a bug, though it's not clear which should be changed. -One option is to change mkcramfs to take its PAGE_CACHE_SIZE from +One option is to change mkcramfs to take its PAGE_SIZE from <asm/page.h>. Personally I don't like this option, but it does require the least amount of change: just change `#define -PAGE_CACHE_SIZE (4096)' to `#include <asm/page.h>'. The disadvantage +PAGE_SIZE (4096)' to `#include <asm/page.h>'. The disadvantage is that the generated cramfs cannot always be shared between different kernels, not even necessarily kernels of the same architecture if -PAGE_CACHE_SIZE is subject to change between kernel versions +PAGE_SIZE is subject to change between kernel versions (currently possible with arm and ia64). The remaining options try to make cramfs more sharable. @@ -126,22 +126,22 @@ size. The options are: 1. Always 4096 bytes. 2. Writer chooses blocksize; kernel adapts but rejects blocksize > - PAGE_CACHE_SIZE. + PAGE_SIZE. 3. Writer chooses blocksize; kernel adapts even to blocksize > - PAGE_CACHE_SIZE. + PAGE_SIZE. It's easy enough to change the kernel to use a smaller value than -PAGE_CACHE_SIZE: just make cramfs_readpage read multiple blocks. +PAGE_SIZE: just make cramfs_readpage read multiple blocks. -The cost of option 1 is that kernels with a larger PAGE_CACHE_SIZE +The cost of option 1 is that kernels with a larger PAGE_SIZE value don't get as good compression as they can. The cost of option 2 relative to option 1 is that the code uses variables instead of #define'd constants. The gain is that people -with kernels having larger PAGE_CACHE_SIZE can make use of that if +with kernels having larger PAGE_SIZE can make use of that if they don't mind their cramfs being inaccessible to kernels with -smaller PAGE_CACHE_SIZE values. +smaller PAGE_SIZE values. Option 3 is easy to implement if we don't mind being CPU-inefficient: e.g. get readpage to decompress to a buffer of size MAX_BLKSIZE (which |