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    SubjectRe: [PATCH 2/5] jffs2: Add LZO compression support to jffs2
    Hi Richard,

    On 5/1/07, Richard Purdie <rpurdie@openedhand.com> wrote:
    > Add LZO1X compression/decompression support to jffs2.
    >
    > LZO's interface doesn't entirely match that required by jffs2 so a
    > buffer and memcpy is unavoidable.
    >
    > Signed-off-by: Richard Purdie <rpurdie@openedhand.com>
    > ---
    > [...]
    > +++ b/fs/jffs2/compr_lzo.c
    > [...]
    > +static void *lzo_mem;
    > +static void *lzo_compress_buf;
    > +static DEFINE_MUTEX(deflate_mutex);
    > +
    > +static void free_workspace(void)
    > +{
    > + vfree(lzo_mem);
    > + vfree(lzo_compress_buf);
    > +}
    > +
    > +static int __init alloc_workspace(void)
    > +{
    > + lzo_mem = vmalloc(LZO1X_MEM_COMPRESS);
    > + lzo_compress_buf = vmalloc(lzo1x_worst_compress(PAGE_SIZE));
    > +
    > + if (!lzo_mem || !lzo_compress_buf) {
    > + printk(KERN_WARNING "Failed to allocate lzo deflate workspace\n");
    > + free_workspace();
    > + return -ENOMEM;
    > + }
    > +
    > + return 0;
    > +}
    > +
    > +static int jffs2_lzo_compress(unsigned char *data_in, unsigned char *cpage_out,
    > + uint32_t *sourcelen, uint32_t *dstlen, void *model)
    > +{
    > + unsigned long compress_size;
    > + int ret;
    > +
    > + mutex_lock(&deflate_mutex);
    > + ret = lzo1x_1_compress(data_in, *sourcelen, lzo_compress_buf, &compress_size, lzo_mem);
    > + mutex_unlock(&deflate_mutex);

    Considering we do have to memcpy() the entire compressed result to the
    destination output buffer later anyway (note that
    fs/jffs2/compr_zlib.c doesn't need to do that), do we really gain much
    by avoiding vmalloc() and vfree() in jffs2_lzo_compress() itself and
    keeping the workspace buffers pre-allocated? I ask because I always
    found these global static workspace buffers ugly, and all the
    associated code + mutex could go away if we make them local to
    jffs2_lzo_compress() -- as long as it doesn't hurt performance
    terribly, of course.

    Thanks,
    Satyam
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