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    SubjectRe: [PATCH 01/23] Hibernation: Split compression support out.
    Date
    On Monday, September 27, 2010, Nigel Cunningham wrote:
    > Separate compression support out into its own file, removing in
    > the process the duplication of the load_image and save_image
    > functions and some #includes from swap.c that are no longer
    > needed.
    >
    > Signed-off-by: Nigel Cunningham <nigel@tuxonice.net>

    If you're at it, I'd like to do something slightly different. Explained below.

    > ---
    > kernel/power/Makefile | 2 +-
    > kernel/power/compress.c | 210 +++++++++++++++++++++++++++++
    > kernel/power/compress.h | 23 +++
    > kernel/power/swap.c | 339 +++++------------------------------------------
    > kernel/power/swap.h | 28 ++++
    > 5 files changed, 296 insertions(+), 306 deletions(-)
    > create mode 100644 kernel/power/compress.c
    > create mode 100644 kernel/power/compress.h
    > create mode 100644 kernel/power/swap.h
    >
    > diff --git a/kernel/power/Makefile b/kernel/power/Makefile
    > index f9063c6..2eb134d 100644
    > --- a/kernel/power/Makefile
    > +++ b/kernel/power/Makefile
    > @@ -9,7 +9,7 @@ obj-$(CONFIG_FREEZER) += process.o
    > obj-$(CONFIG_SUSPEND) += suspend.o
    > obj-$(CONFIG_PM_TEST_SUSPEND) += suspend_test.o
    > obj-$(CONFIG_HIBERNATION) += hibernate.o snapshot.o swap.o user.o \
    > - block_io.o
    > + block_io.o compress.o
    > obj-$(CONFIG_SUSPEND_NVS) += nvs.o
    >
    > obj-$(CONFIG_MAGIC_SYSRQ) += poweroff.o
    > diff --git a/kernel/power/compress.c b/kernel/power/compress.c
    > new file mode 100644
    > index 0000000..45725ea
    > --- /dev/null
    > +++ b/kernel/power/compress.c
    > @@ -0,0 +1,210 @@
    > +/*
    > + * linux/kernel/power/compress.c
    > + *
    > + * This file provides functions for (optionally) compressing an
    > + * image as it is being written and decompressing it at resume.
    > + *
    > + * Copyright (C) 2003-2010 Nigel Cunningham <nigel@tuxonice.net>
    > + *
    > + * This file is released under the GPLv2.
    > + *
    > + */
    > +
    > +#include <linux/slab.h>
    > +#include <linux/lzo.h>
    > +#include <linux/vmalloc.h>
    > +
    > +#include "power.h"
    > +#include "swap.h"
    > +
    > +/* We need to remember how much compressed data we need to read. */
    > +#define LZO_HEADER sizeof(size_t)
    > +
    > +/* Number of pages/bytes we'll compress at one time. */
    > +#define LZO_UNC_PAGES 32
    > +#define LZO_UNC_SIZE (LZO_UNC_PAGES * PAGE_SIZE)
    > +
    > +/* Number of pages/bytes we need for compressed data (worst case). */
    > +#define LZO_CMP_PAGES DIV_ROUND_UP(lzo1x_worst_compress(LZO_UNC_SIZE) + \
    > + LZO_HEADER, PAGE_SIZE)
    > +#define LZO_CMP_SIZE (LZO_CMP_PAGES * PAGE_SIZE)
    > +
    > +static size_t off, unc_len, cmp_len;
    > +static unsigned char *unc, *cmp, *wrk, *page;
    > +
    > +void compress_image_cleanup(void)
    > +{
    > + if (cmp) {
    > + vfree(cmp);
    > + cmp = NULL;
    > + }
    > +
    > + if (unc) {
    > + vfree(unc);
    > + unc = NULL;
    > + }
    > +
    > + if (wrk) {
    > + vfree(wrk);
    > + wrk = NULL;
    > + }
    > +
    > + if (page) {
    > + free_page((unsigned long)page);
    > + page = NULL;
    > + }
    > +}
    > +
    > +int compress_image_init(void)
    > +{
    > + page = (void *)__get_free_page(__GFP_WAIT | __GFP_HIGH);
    > + if (!page) {
    > + printk(KERN_ERR "PM: Failed to allocate LZO page\n");
    > + return -ENOMEM;
    > + }
    > +
    > + wrk = vmalloc(LZO1X_1_MEM_COMPRESS);
    > + unc = vmalloc(LZO_UNC_SIZE);
    > + cmp = vmalloc(LZO_CMP_SIZE);
    > +
    > + if (!wrk || !unc || !cmp) {
    > + printk(KERN_ERR "PM: Failed to allocate memory for (de)compression.\n");
    > + compress_image_cleanup();
    > + return -ENOMEM;
    > + }
    > +
    > + off = 0;
    > +
    > + return 0;
    > +}
    > +
    > +static int compress_and_write(struct swap_map_handle *handle, struct bio **bio)
    > +{
    > + int ret;
    > +
    > + if (!off)
    > + return 0;
    > +
    > + unc_len = off;
    > + ret = lzo1x_1_compress(unc, unc_len, cmp + LZO_HEADER, &cmp_len, wrk);
    > +
    > + if (ret < 0) {
    > + printk(KERN_ERR "PM: LZO compression failed\n");
    > + return -EIO;
    > + }
    > +
    > + if (unlikely(!cmp_len ||
    > + cmp_len > lzo1x_worst_compress(unc_len))) {
    > + printk(KERN_ERR "PM: Invalid LZO compressed length\n");
    > + return -EIO;
    > + }
    > +
    > + *(size_t *)cmp = cmp_len;
    > +
    > + /*
    > + * Given we are writing one page at a time to disk, we copy
    > + * that much from the buffer, although the last bit will likely
    > + * be smaller than full page. This is OK - we saved the length
    > + * of the compressed data, so any garbage at the end will be
    > + * discarded when we read it.
    > + */
    > + for (off = 0; off < LZO_HEADER + cmp_len; off += PAGE_SIZE) {
    > + memcpy(page, cmp + off, PAGE_SIZE);
    > +
    > + ret = swap_write_page(handle, page, bio);
    > + if (ret)
    > + return ret;
    > + }
    > +
    > + off = 0;
    > + return 0;
    > +}
    > +
    > +int compress_write(struct swap_map_handle *handle, char *buf, struct bio **bio,
    > + int flags)
    > +{
    > + int ret = 0;
    > +
    > + if (flags & SF_NOCOMPRESS_MODE)
    > + return swap_write_page(handle, buf, bio);
    > +
    > + if (off == LZO_UNC_SIZE)
    > + ret = compress_and_write(handle, bio);
    > +
    > + memcpy(unc + off, buf, PAGE_SIZE);
    > + off += PAGE_SIZE;
    > + return ret;
    > +}

    This one doesn't really good to me. What I'd prefer would be to have a
    structure of "swap operations" pointers like ->start(), ->write_data(),
    ->read_data(), and ->finish() that will point to the functions in this file
    (if compression is to be used) or to the "old" swap_write_page()/swap_read_page()
    otherwise. That would reduce the number of the
    (flags & SF_NOCOMPRESS_MODE) checks quite substantially and will likely result
    in code that's easier to follow.

    Thanks,
    Rafael


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