From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-99.freemail.mail.aliyun.com (out30-99.freemail.mail.aliyun.com [115.124.30.99]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 150D12192FF; Wed, 26 Feb 2025 15:07:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.99 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740582446; cv=none; b=PeLBiHFumgkbxkCAX0Q/rSeL+Mq7MZssdUjlfuwPc5t3MrWqXh2dNAqFLSsIBdFN3Qrm5PSSd+SExTlGFIVxvITPsz3NsNOg9LnS6kP9zjO7QiFGzmXAIstmdLg6K69lzC4EabxcwIdibXw7MjFYMzWGc2k65eCZ8sdPmRIFnXA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740582446; c=relaxed/simple; bh=HCxvtMmD0q8Ecc6j8XnWICZNS4c5H5ShgZnuBdCAUfY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=qG532ijdry8uRxfONeWcJL4ze4hNOv+3TwV4bCVg1XZIZ664dwuMZPfqeMTWGhwRRJ8u6BeOS5yyHFyr+gzho2rmQUx7Hk7HkrZHFiiGtxUMt9QTR7Pu8HgA9uigpOP9tPiELVaWXQWRxtPc+9eosnMmKGJB84jVBd8FOtT+d2U= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=TzKoC1CO; arc=none smtp.client-ip=115.124.30.99 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="TzKoC1CO" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1740582433; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=2rTvbSpIOmTKBaiNFLCvfmk2C0D9YajUNAGPaB59Boo=; b=TzKoC1COaQsJqy6YU+UqPvFdoNethSUGtAsR+q2xAEc0xxPK9JzaNGkYBSmZAerrGX/j+afJar/J6kYRMJNs/qzoVNI/6y0Zmh/6R5wcvS7lkH5AaP9IZfirxN5r5GUqHwUWeh1NxlZnTFk9dARYAhbugbTUSJAfiDnSKEedZck= Received: from 30.39.248.98(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0WQJGQ7I_1740582431 cluster:ay36) by smtp.aliyun-inc.com; Wed, 26 Feb 2025 23:07:12 +0800 Message-ID: <3cda74d5-ae82-4f7b-844f-b14e146dc60a@linux.alibaba.com> Date: Wed, 26 Feb 2025 23:07:09 +0800 Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v8 1/8] xarray: add xas_try_split() to split a multi-index entry To: Zi Yan Cc: linux-mm@kvack.org, Andrew Morton , "Kirill A . Shutemov" , "Matthew Wilcox (Oracle)" , Ryan Roberts , Hugh Dickins , David Hildenbrand , Yang Shi , Miaohe Lin , Kefeng Wang , Yu Zhao , John Hubbard , linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org References: <20250218235012.1542225-1-ziy@nvidia.com> <20250218235012.1542225-2-ziy@nvidia.com> <8FC0353E-EB2D-4C4C-B96D-8BEC06FE77F7@nvidia.com> From: Baolin Wang In-Reply-To: <8FC0353E-EB2D-4C4C-B96D-8BEC06FE77F7@nvidia.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 2025/2/26 23:00, Zi Yan wrote: > On 26 Feb 2025, at 2:11, Baolin Wang wrote: > >> Hi Zi, >> >> On 2025/2/19 07:50, Zi Yan wrote: >>> A preparation patch for non-uniform folio split, which always split a >>> folio into half iteratively, and minimal xarray entry split. >>> >>> Currently, xas_split_alloc() and xas_split() always split all slots from a >>> multi-index entry. They cost the same number of xa_node as the >>> to-be-split slots. For example, to split an order-9 entry, which takes >>> 2^(9-6)=8 slots, assuming XA_CHUNK_SHIFT is 6 (!CONFIG_BASE_SMALL), 8 >>> xa_node are needed. Instead xas_try_split() is intended to be used >>> iteratively to split the order-9 entry into 2 order-8 entries, then split >>> one order-8 entry, based on the given index, to 2 order-7 entries, ..., >>> and split one order-1 entry to 2 order-0 entries. When splitting the >>> order-6 entry and a new xa_node is needed, xas_try_split() will try to >>> allocate one if possible. As a result, xas_try_split() would only need >>> one xa_node instead of 8. >>> >>> When a new xa_node is needed during the split, xas_try_split() can try to >>> allocate one but no more. -ENOMEM will be return if a node cannot be >>> allocated. -EINVAL will be return if a sibling node is split or cascade >>> split happens, where two or more new nodes are needed, and these are not >>> supported by xas_try_split(). >>> >>> xas_split_alloc() and xas_split() split an order-9 to order-0: >>> >>> --------------------------------- >>> | | | | | | | | | >>> | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | >>> | | | | | | | | | >>> --------------------------------- >>> | | | | >>> ------- --- --- ------- >>> | | ... | | >>> V V V V >>> ----------- ----------- ----------- ----------- >>> | xa_node | | xa_node | ... | xa_node | | xa_node | >>> ----------- ----------- ----------- ----------- >>> >>> xas_try_split() splits an order-9 to order-0: >>> --------------------------------- >>> | | | | | | | | | >>> | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | >>> | | | | | | | | | >>> --------------------------------- >>> | >>> | >>> V >>> ----------- >>> | xa_node | >>> ----------- >>> >>> Signed-off-by: Zi Yan >>> Cc: Baolin Wang >>> Cc: David Hildenbrand >>> Cc: Hugh Dickins >>> Cc: John Hubbard >>> Cc: Kefeng Wang >>> Cc: Kirill A. Shuemov >>> Cc: Miaohe Lin >>> Cc: Matthew Wilcox >>> Cc: Ryan Roberts >>> Cc: Yang Shi >>> Cc: Yu Zhao >>> Cc: Zi Yan >>> --- >>> Documentation/core-api/xarray.rst | 14 ++- >>> include/linux/xarray.h | 7 ++ >>> lib/test_xarray.c | 47 ++++++++++ >>> lib/xarray.c | 138 ++++++++++++++++++++++++++---- >>> tools/testing/radix-tree/Makefile | 1 + >>> 5 files changed, 190 insertions(+), 17 deletions(-) >>> >>> diff --git a/Documentation/core-api/xarray.rst b/Documentation/core-api/xarray.rst >>> index f6a3eef4fe7f..c6c91cbd0c3c 100644 >>> --- a/Documentation/core-api/xarray.rst >>> +++ b/Documentation/core-api/xarray.rst >>> @@ -489,7 +489,19 @@ Storing ``NULL`` into any index of a multi-index entry will set the >>> entry at every index to ``NULL`` and dissolve the tie. A multi-index >>> entry can be split into entries occupying smaller ranges by calling >>> xas_split_alloc() without the xa_lock held, followed by taking the lock >>> -and calling xas_split(). >>> +and calling xas_split() or calling xas_try_split() with xa_lock. The >>> +difference between xas_split_alloc()+xas_split() and xas_try_alloc() is >>> +that xas_split_alloc() + xas_split() split the entry from the original >>> +order to the new order in one shot uniformly, whereas xas_try_split() >>> +iteratively splits the entry containing the index non-uniformly. >>> +For example, to split an order-9 entry, which takes 2^(9-6)=8 slots, >>> +assuming ``XA_CHUNK_SHIFT`` is 6, xas_split_alloc() + xas_split() need >>> +8 xa_node. xas_try_split() splits the order-9 entry into >>> +2 order-8 entries, then split one order-8 entry, based on the given index, >>> +to 2 order-7 entries, ..., and split one order-1 entry to 2 order-0 entries. >>> +When splitting the order-6 entry and a new xa_node is needed, xas_try_split() >>> +will try to allocate one if possible. As a result, xas_try_split() would only >>> +need 1 xa_node instead of 8. >>> Functions and structures >>> ======================== >>> diff --git a/include/linux/xarray.h b/include/linux/xarray.h >>> index 0b618ec04115..9eb8c7425090 100644 >>> --- a/include/linux/xarray.h >>> +++ b/include/linux/xarray.h >>> @@ -1555,6 +1555,8 @@ int xa_get_order(struct xarray *, unsigned long index); >>> int xas_get_order(struct xa_state *xas); >>> void xas_split(struct xa_state *, void *entry, unsigned int order); >>> void xas_split_alloc(struct xa_state *, void *entry, unsigned int order, gfp_t); >>> +void xas_try_split(struct xa_state *xas, void *entry, unsigned int order, >>> + gfp_t gfp); >>> #else >>> static inline int xa_get_order(struct xarray *xa, unsigned long index) >>> { >>> @@ -1576,6 +1578,11 @@ static inline void xas_split_alloc(struct xa_state *xas, void *entry, >>> unsigned int order, gfp_t gfp) >>> { >>> } >>> + >>> +static inline void xas_try_split(struct xa_state *xas, void *entry, >>> + unsigned int order, gfp_t gfp) >>> +{ >>> +} >>> #endif >>> /** >> >> [snip] >> >>> diff --git a/lib/xarray.c b/lib/xarray.c >>> index 116e9286c64e..b9a63d7fbd58 100644 >>> --- a/lib/xarray.c >>> +++ b/lib/xarray.c >>> @@ -1007,6 +1007,31 @@ static void node_set_marks(struct xa_node *node, unsigned int offset, >>> } >>> } >>> +static struct xa_node *__xas_alloc_node_for_split(struct xa_state *xas, >>> + void *entry, gfp_t gfp) >>> +{ >>> + unsigned int i; >>> + void *sibling = NULL; >>> + struct xa_node *node; >>> + unsigned int mask = xas->xa_sibs; >>> + >>> + node = kmem_cache_alloc_lru(radix_tree_node_cachep, xas->xa_lru, gfp); >>> + if (!node) >>> + return NULL; >>> + node->array = xas->xa; >>> + for (i = 0; i < XA_CHUNK_SIZE; i++) { >>> + if ((i & mask) == 0) { >>> + RCU_INIT_POINTER(node->slots[i], entry); >>> + sibling = xa_mk_sibling(i); >>> + } else { >>> + RCU_INIT_POINTER(node->slots[i], sibling); >>> + } >>> + } >>> + RCU_INIT_POINTER(node->parent, xas->xa_alloc); >>> + >>> + return node; >>> +} >>> + >>> /** >>> * xas_split_alloc() - Allocate memory for splitting an entry. >>> * @xas: XArray operation state. >>> @@ -1025,7 +1050,6 @@ void xas_split_alloc(struct xa_state *xas, void *entry, unsigned int order, >>> gfp_t gfp) >>> { >>> unsigned int sibs = (1 << (order % XA_CHUNK_SHIFT)) - 1; >>> - unsigned int mask = xas->xa_sibs; >>> /* XXX: no support for splitting really large entries yet */ >>> if (WARN_ON(xas->xa_shift + 2 * XA_CHUNK_SHIFT <= order)) >>> @@ -1034,23 +1058,9 @@ void xas_split_alloc(struct xa_state *xas, void *entry, unsigned int order, >>> return; >>> do { >>> - unsigned int i; >>> - void *sibling = NULL; >>> - struct xa_node *node; >>> - >>> - node = kmem_cache_alloc_lru(radix_tree_node_cachep, xas->xa_lru, gfp); >>> + struct xa_node *node = __xas_alloc_node_for_split(xas, entry, gfp); >>> if (!node) >>> goto nomem; >>> - node->array = xas->xa; >>> - for (i = 0; i < XA_CHUNK_SIZE; i++) { >>> - if ((i & mask) == 0) { >>> - RCU_INIT_POINTER(node->slots[i], entry); >>> - sibling = xa_mk_sibling(i); >>> - } else { >>> - RCU_INIT_POINTER(node->slots[i], sibling); >>> - } >>> - } >>> - RCU_INIT_POINTER(node->parent, xas->xa_alloc); >>> xas->xa_alloc = node; >>> } while (sibs-- > 0); >>> @@ -1122,6 +1132,102 @@ void xas_split(struct xa_state *xas, void *entry, unsigned int order) >>> xas_update(xas, node); >>> } >>> EXPORT_SYMBOL_GPL(xas_split); >>> + >>> +/** >>> + * xas_try_split() - Try to split a multi-index entry. >>> + * @xas: XArray operation state. >>> + * @entry: New entry to store in the array. >>> + * @order: Current entry order. >>> + * @gfp: Memory allocation flags. >>> + * >>> + * The size of the new entries is set in @xas. The value in @entry is >>> + * copied to all the replacement entries. If and only if one xa_node needs to >>> + * be allocated, the function will use @gfp to get one. If more xa_node are >>> + * needed, the function gives EINVAL error. >>> + * >>> + * Context: Any context. The caller should hold the xa_lock. >>> + */ >>> +void xas_try_split(struct xa_state *xas, void *entry, unsigned int order, >>> + gfp_t gfp) >> >> The xas_try_split() may sleep if ‘gfp’ flags permit while holding the xa_lock, which can cause issues. So can we add a check for the ‘gfp’ or only use GFP_NOWAIT? > > You mean only allow gfp to be GFP_NOWAIT or GFP_ATOMIC? Yes.