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Message-ID: <84144f020908241033l4af09e7h9caac47d8d9b7841@mail.gmail.com>
Date: Mon, 24 Aug 2009 20:33:25 +0300
From: Pekka Enberg <penberg@...helsinki.fi>
To: ngupta@...are.org
Cc: akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, linux-mm-cc@...top.org
Subject: Re: [PATCH 1/4] compcache: xvmalloc memory allocator
Hi Nitin,
[ Nit: the name xmalloc() is usually reserved for non-failing allocators in
user-space which is why xvmalloc() looks so confusing to me. Can we
get a better name for the thing? Also, I'm not sure why xvmalloc is a
separate module. Can't you just make it in-kernel or compile it in to the
ramzswap module? ]
On Mon, Aug 24, 2009 at 7:37 AM, Nitin Gupta<ngupta@...are.org> wrote:
> +/**
> + * xv_malloc - Allocate block of given size from pool.
> + * @pool: pool to allocate from
> + * @size: size of block to allocate
> + * @pagenum: page no. that holds the object
> + * @offset: location of object within pagenum
> + *
> + * On success, <pagenum, offset> identifies block allocated
> + * and 0 is returned. On failure, <pagenum, offset> is set to
> + * 0 and -ENOMEM is returned.
> + *
> + * Allocation requests with size > XV_MAX_ALLOC_SIZE will fail.
> + */
> +int xv_malloc(struct xv_pool *pool, u32 size, u32 *pagenum, u32 *offset,
> + gfp_t flags)
> +{
> + int error;
> + u32 index, tmpsize, origsize, tmpoffset;
> + struct block_header *block, *tmpblock;
> +
> + *pagenum = 0;
> + *offset = 0;
> + origsize = size;
> +
> + if (unlikely(!size || size > XV_MAX_ALLOC_SIZE))
> + return -ENOMEM;
> +
> + size = ALIGN(size, XV_ALIGN);
> +
> + spin_lock(&pool->lock);
> +
> + index = find_block(pool, size, pagenum, offset);
> +
> + if (!*pagenum) {
> + spin_unlock(&pool->lock);
> + if (flags & GFP_NOWAIT)
> + return -ENOMEM;
> + error = grow_pool(pool, flags);
> + if (unlikely(error))
> + return -ENOMEM;
> +
> + spin_lock(&pool->lock);
> + index = find_block(pool, size, pagenum, offset);
> + }
> +
> + if (!*pagenum) {
> + spin_unlock(&pool->lock);
> + return -ENOMEM;
> + }
> +
> + block = get_ptr_atomic(*pagenum, *offset, KM_USER0);
> +
> + remove_block_head(pool, block, index);
> +
> + /* Split the block if required */
> + tmpoffset = *offset + size + XV_ALIGN;
> + tmpsize = block->size - size;
> + tmpblock = (struct block_header *)((char *)block + size + XV_ALIGN);
> + if (tmpsize) {
> + tmpblock->size = tmpsize - XV_ALIGN;
> + set_flag(tmpblock, BLOCK_FREE);
> + clear_flag(tmpblock, PREV_FREE);
> +
> + set_blockprev(tmpblock, *offset);
> + if (tmpblock->size >= XV_MIN_ALLOC_SIZE)
> + insert_block(pool, *pagenum, tmpoffset, tmpblock);
> +
> + if (tmpoffset + XV_ALIGN + tmpblock->size != PAGE_SIZE) {
> + tmpblock = BLOCK_NEXT(tmpblock);
> + set_blockprev(tmpblock, tmpoffset);
> + }
> + } else {
> + /* This block is exact fit */
> + if (tmpoffset != PAGE_SIZE)
> + clear_flag(tmpblock, PREV_FREE);
> + }
> +
> + block->size = origsize;
> + clear_flag(block, BLOCK_FREE);
> +
> + put_ptr_atomic(block, KM_USER0);
> + spin_unlock(&pool->lock);
> +
> + *offset += XV_ALIGN;
> +
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(xv_malloc);
What's the purpose of passing PFNs around? There's quite a lot of PFN
to struct page conversion going on because of it. Wouldn't it make
more sense to return (and pass) a pointer to struct page instead?
Pekka
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