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Date: Sat, 29 Jun 2024 19:15:39 +0800
From: Yunsheng Lin <linyunsheng@...wei.com>
To: Alexander H Duyck <alexander.duyck@...il.com>, <davem@...emloft.net>,
<kuba@...nel.org>, <pabeni@...hat.com>
CC: <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>, Andrew Morton
<akpm@...ux-foundation.org>, <linux-mm@...ck.org>
Subject: Re: [PATCH net-next v9 10/13] mm: page_frag: introduce
prepare/probe/commit API
On 2024/6/29 6:35, Alexander H Duyck wrote:
> On Tue, 2024-06-25 at 21:52 +0800, Yunsheng Lin wrote:
>> There are many use cases that need minimum memory in order
>> for forward progress, but more performant if more memory is
>> available or need to probe the cache info to use any memory
>> available for frag caoleasing reason.
>>
>> Currently skb_page_frag_refill() API is used to solve the
>> above use cases, but caller needs to know about the internal
>> detail and access the data field of 'struct page_frag' to
>> meet the requirement of the above use cases and its
>> implementation is similar to the one in mm subsystem.
>>
>> To unify those two page_frag implementations, introduce a
>> prepare API to ensure minimum memory is satisfied and return
>> how much the actual memory is available to the caller and a
>> probe API to report the current available memory to caller
>> without doing cache refilling. The caller needs to either call
>> the commit API to report how much memory it actually uses, or
>> not do so if deciding to not use any memory.
>>
>> As next patch is about to replace 'struct page_frag' with
>> 'struct page_frag_cache' in linux/sched.h, which is included
>> by the asm-offsets.s, using the virt_to_page() in the inline
>> helper of page_frag_cache.h cause a "'vmemmap' undeclared"
>> compiling error for asm-offsets.s, use a macro for probe API
>> to avoid that compiling error.
>>
>> CC: Alexander Duyck <alexander.duyck@...il.com>
>> Signed-off-by: Yunsheng Lin <linyunsheng@...wei.com>
>> ---
>> include/linux/page_frag_cache.h | 82 +++++++++++++++++++++++
>> mm/page_frag_cache.c | 114 ++++++++++++++++++++++++++++++++
>> 2 files changed, 196 insertions(+)
>>
>> diff --git a/include/linux/page_frag_cache.h b/include/linux/page_frag_cache.h
>> index b33904d4494f..e95d44a36ec9 100644
>> --- a/include/linux/page_frag_cache.h
>> +++ b/include/linux/page_frag_cache.h
>> @@ -4,6 +4,7 @@
>> #define _LINUX_PAGE_FRAG_CACHE_H
>>
>> #include <linux/gfp_types.h>
>> +#include <linux/mmdebug.h>
>>
>> #define PAGE_FRAG_CACHE_MAX_SIZE __ALIGN_MASK(32768, ~PAGE_MASK)
>> #define PAGE_FRAG_CACHE_MAX_ORDER get_order(PAGE_FRAG_CACHE_MAX_SIZE)
>> @@ -87,6 +88,9 @@ static inline unsigned int page_frag_cache_page_size(struct encoded_va *encoded_
>>
>> void page_frag_cache_drain(struct page_frag_cache *nc);
>> void __page_frag_cache_drain(struct page *page, unsigned int count);
>> +struct page *page_frag_alloc_pg(struct page_frag_cache *nc,
>> + unsigned int *offset, unsigned int fragsz,
>> + gfp_t gfp);
>> void *__page_frag_alloc_va_align(struct page_frag_cache *nc,
>> unsigned int fragsz, gfp_t gfp_mask,
>> unsigned int align_mask);
>> @@ -99,12 +103,90 @@ static inline void *page_frag_alloc_va_align(struct page_frag_cache *nc,
>> return __page_frag_alloc_va_align(nc, fragsz, gfp_mask, -align);
>> }
>>
>> +static inline unsigned int page_frag_cache_page_offset(const struct page_frag_cache *nc)
>> +{
>> + return page_frag_cache_page_size(nc->encoded_va) - nc->remaining;
>> +}
>> +
>> static inline void *page_frag_alloc_va(struct page_frag_cache *nc,
>> unsigned int fragsz, gfp_t gfp_mask)
>> {
>> return __page_frag_alloc_va_align(nc, fragsz, gfp_mask, ~0u);
>> }
>>
>> +void *page_frag_alloc_va_prepare(struct page_frag_cache *nc, unsigned int *fragsz,
>> + gfp_t gfp);
>> +
>> +static inline void *page_frag_alloc_va_prepare_align(struct page_frag_cache *nc,
>> + unsigned int *fragsz,
>> + gfp_t gfp,
>> + unsigned int align)
>> +{
>> + WARN_ON_ONCE(!is_power_of_2(align) || align > PAGE_SIZE);
>> + nc->remaining = nc->remaining & -align;
>> + return page_frag_alloc_va_prepare(nc, fragsz, gfp);
>> +}
>> +
>> +struct page *page_frag_alloc_pg_prepare(struct page_frag_cache *nc,
>> + unsigned int *offset,
>> + unsigned int *fragsz, gfp_t gfp);
>> +
>> +struct page *page_frag_alloc_prepare(struct page_frag_cache *nc,
>> + unsigned int *offset,
>> + unsigned int *fragsz,
>> + void **va, gfp_t gfp);
>> +
>> +static inline struct encoded_va *__page_frag_alloc_probe(struct page_frag_cache *nc,
>> + unsigned int *offset,
>> + unsigned int *fragsz,
>> + void **va)
>> +{
>> + struct encoded_va *encoded_va;
>> +
>> + *fragsz = nc->remaining;
>> + encoded_va = nc->encoded_va;
>> + *offset = page_frag_cache_page_size(encoded_va) - *fragsz;
>> + *va = encoded_page_address(encoded_va) + *offset;
>> +
>> + return encoded_va;
>> +}
>> +
>> +#define page_frag_alloc_probe(nc, offset, fragsz, va) \
>> +({ \
>> + struct page *__page = NULL; \
>> + \
>> + VM_BUG_ON(!*(fragsz)); \
>> + if (likely((nc)->remaining >= *(fragsz))) \
>> + __page = virt_to_page(__page_frag_alloc_probe(nc, \
>> + offset, \
>> + fragsz, \
>> + va)); \
>> + \
>> + __page; \
>> +})
>> +
>
> Why is this a macro instead of just being an inline? Are you trying to
> avoid having to include a header due to the virt_to_page?
Yes, you are right.
I tried including different headers for virt_to_page(), and it did not
work for arch/x86/kernel/asm-offsets.s, which has included linux/sched.h,
and linux/sched.h need 'struct page_frag_cache' for 'struct task_struct'
after this patchset, including page_frag_cache.h for sched.h causes the
below compiler error:
CC arch/x86/kernel/asm-offsets.s
In file included from ./arch/x86/include/asm/page.h:89,
from ./arch/x86/include/asm/thread_info.h:12,
from ./include/linux/thread_info.h:60,
from ./include/linux/spinlock.h:60,
from ./include/linux/swait.h:7,
from ./include/linux/completion.h:12,
from ./include/linux/crypto.h:15,
from arch/x86/kernel/asm-offsets.c:9:
./include/linux/page_frag_cache.h: In function ‘page_frag_alloc_align’:
./include/asm-generic/memory_model.h:37:34: error: ‘vmemmap’ undeclared (first use in this function); did you mean ‘mem_map’?
37 | #define __pfn_to_page(pfn) (vmemmap + (pfn))
| ^~~~~~~
./include/asm-generic/memory_model.h:65:21: note: in expansion of macro ‘__pfn_to_page’
65 | #define pfn_to_page __pfn_to_page
| ^~~~~~~~~~~~~
./arch/x86/include/asm/page.h:68:33: note: in expansion of macro ‘pfn_to_page’
68 | #define virt_to_page(kaddr) pfn_to_page(__pa(kaddr) >> PAGE_SHIFT)
| ^~~~~~~~~~~
./include/linux/page_frag_cache.h:151:16: note: in expansion of macro ‘virt_to_page’
151 | return virt_to_page(va);
| ^~~~~~~~~~~~
./include/asm-generic/memory_model.h:37:34: note: each undeclared identifier is reported only once for each function it appears in
37 | #define __pfn_to_page(pfn) (vmemmap + (pfn))
| ^~~~~~~
./include/asm-generic/memory_model.h:65:21: note: in expansion of macro ‘__pfn_to_page’
65 | #define pfn_to_page __pfn_to_page
| ^~~~~~~~~~~~~
./arch/x86/include/asm/page.h:68:33: note: in expansion of macro ‘pfn_to_page’
68 | #define virt_to_page(kaddr) pfn_to_page(__pa(kaddr) >> PAGE_SHIFT)
| ^~~~~~~~~~~
./include/linux/page_frag_cache.h:151:16: note: in expansion of macro ‘virt_to_page’
151 | return virt_to_page(va);
Another possible way I can think of to aovid the above problem is to
split the page_frag_cache.h to something like page_frag_cache/types.h
and page_frag_cache/helpers.h as page_pool does, so that sched.h only
need to include page_frag_cache/types.h.
But I am not sure it is the correct way or it is worth the effort, what
do you think about this?
>
> .
>
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