[PATCH v3] f2fs: avoid splitting bio when reading multiple pages

[PATCH v3] f2fs: avoid splitting bio when reading multiple pages

[Jianan Huang]

When fewer pages are read, nr_pages may be smaller than nr_cpages. Due
to the nr_vecs limit, the compressed pages will be split into multiple
bios and then merged at the block level. In this case, nr_cpages should
be used to pre-allocate bvecs.
To handle this case, align max_nr_pages to cluster_size, which should be
enough for all compressed pages.

Signed-off-by: Jianan Huang <huangjianan@xiaomi.com>
Signed-off-by: Sheng Yong <shengyong1@xiaomi.com>
---
Changes since v2:
- Initialize index only for compressed files.
Changes since v1:
- Use aligned nr_pages instead of nr_cpages to pre-allocate bvecs.

 fs/f2fs/data.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 31e892842625..d071d9f6a811 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -2303,7 +2303,7 @@ int f2fs_read_multi_pages(struct compress_ctx *cc, struct bio **bio_ret,
 		}
 
 		if (!bio) {
-			bio = f2fs_grab_read_bio(inode, blkaddr, nr_pages,
+			bio = f2fs_grab_read_bio(inode, blkaddr, nr_pages - i,
 					f2fs_ra_op_flags(rac),
 					folio->index, for_write);
 			if (IS_ERR(bio)) {
@@ -2376,6 +2376,14 @@ static int f2fs_mpage_readpages(struct inode *inode,
 	unsigned max_nr_pages = nr_pages;
 	int ret = 0;
 
+#ifdef CONFIG_F2FS_FS_COMPRESSION
+	if (f2fs_compressed_file(inode)) {
+		index = rac ? readahead_index(rac) : folio->index;
+		max_nr_pages = round_up(index + nr_pages, cc.cluster_size) -
+				round_down(index, cc.cluster_size);
+	}
+#endif
+
 	map.m_pblk = 0;
 	map.m_lblk = 0;
 	map.m_len = 0;
@@ -2385,7 +2393,7 @@ static int f2fs_mpage_readpages(struct inode *inode,
 	map.m_seg_type = NO_CHECK_TYPE;
 	map.m_may_create = false;
 
-	for (; nr_pages; nr_pages--) {
+	for (; nr_pages; nr_pages--, max_nr_pages--) {
 		if (rac) {
 			folio = readahead_folio(rac);
 			prefetchw(&folio->flags);
-- 
2.43.0

Re: [PATCH v3] f2fs: avoid splitting bio when reading multiple pages

[Chao Yu]

On 6/25/25 14:49, Jianan Huang wrote:
> When fewer pages are read, nr_pages may be smaller than nr_cpages. Due
> to the nr_vecs limit, the compressed pages will be split into multiple
> bios and then merged at the block level. In this case, nr_cpages should
> be used to pre-allocate bvecs.
> To handle this case, align max_nr_pages to cluster_size, which should be
> enough for all compressed pages.
> 
> Signed-off-by: Jianan Huang <huangjianan@xiaomi.com>
> Signed-off-by: Sheng Yong <shengyong1@xiaomi.com>
> ---
> Changes since v2:
> - Initialize index only for compressed files.
> Changes since v1:
> - Use aligned nr_pages instead of nr_cpages to pre-allocate bvecs.
> 
>  fs/f2fs/data.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index 31e892842625..d071d9f6a811 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -2303,7 +2303,7 @@ int f2fs_read_multi_pages(struct compress_ctx *cc, struct bio **bio_ret,
>  		}
>  
>  		if (!bio) {
> -			bio = f2fs_grab_read_bio(inode, blkaddr, nr_pages,
> +			bio = f2fs_grab_read_bio(inode, blkaddr, nr_pages - i,

Jianan,

Another case:

read page #0,1,2,3 from block #1000,1001,1002, cluster_size=4.

nr_pages=4
max_nr_pages=round_up(0+4,4)-round_down(0,4)=4

f2fs_mpage_readpages() calls f2fs_read_multi_pages() when nr_pages=1, at
that time, max_nr_pages equals to 1 as well.

f2fs_grab_read_bio(..., 1 - 0,...) allocate bio w/ 1 vec capacity, however,
we need at least 3 vecs to merge all cpages, right?

Thanks,

>  					f2fs_ra_op_flags(rac),
>  					folio->index, for_write);
>  			if (IS_ERR(bio)) {
> @@ -2376,6 +2376,14 @@ static int f2fs_mpage_readpages(struct inode *inode,
>  	unsigned max_nr_pages = nr_pages;
>  	int ret = 0;
>  
> +#ifdef CONFIG_F2FS_FS_COMPRESSION
> +	if (f2fs_compressed_file(inode)) {
> +		index = rac ? readahead_index(rac) : folio->index;
> +		max_nr_pages = round_up(index + nr_pages, cc.cluster_size) -
> +				round_down(index, cc.cluster_size);
> +	}
> +#endif
> +
>  	map.m_pblk = 0;
>  	map.m_lblk = 0;
>  	map.m_len = 0;
> @@ -2385,7 +2393,7 @@ static int f2fs_mpage_readpages(struct inode *inode,
>  	map.m_seg_type = NO_CHECK_TYPE;
>  	map.m_may_create = false;
>  
> -	for (; nr_pages; nr_pages--) {
> +	for (; nr_pages; nr_pages--, max_nr_pages--) {
>  		if (rac) {
>  			folio = readahead_folio(rac);
>  			prefetchw(&folio->flags);

Re: [External Mail]Re: [PATCH v3] f2fs: avoid splitting bio when reading multiple pages

[Huang Jianan]

On 2025/6/25 16:45, Chao Yu wrote:
> 
> On 6/25/25 14:49, Jianan Huang wrote:
>> When fewer pages are read, nr_pages may be smaller than nr_cpages. Due
>> to the nr_vecs limit, the compressed pages will be split into multiple
>> bios and then merged at the block level. In this case, nr_cpages should
>> be used to pre-allocate bvecs.
>> To handle this case, align max_nr_pages to cluster_size, which should be
>> enough for all compressed pages.
>>
>> Signed-off-by: Jianan Huang <huangjianan@xiaomi.com>
>> Signed-off-by: Sheng Yong <shengyong1@xiaomi.com>
>> ---
>> Changes since v2:
>> - Initialize index only for compressed files.
>> Changes since v1:
>> - Use aligned nr_pages instead of nr_cpages to pre-allocate bvecs.
>>
>>   fs/f2fs/data.c | 12 ++++++++++--
>>   1 file changed, 10 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
>> index 31e892842625..d071d9f6a811 100644
>> --- a/fs/f2fs/data.c
>> +++ b/fs/f2fs/data.c
>> @@ -2303,7 +2303,7 @@ int f2fs_read_multi_pages(struct compress_ctx *cc, struct bio **bio_ret,
>>                }
>>
>>                if (!bio) {
>> -                     bio = f2fs_grab_read_bio(inode, blkaddr, nr_pages,
>> +                     bio = f2fs_grab_read_bio(inode, blkaddr, nr_pages - i,
> 
> Jianan,
> 
> Another case:
> 
> read page #0,1,2,3 from block #1000,1001,1002, cluster_size=4.
> 
> nr_pages=4
> max_nr_pages=round_up(0+4,4)-round_down(0,4)=4
> 
> f2fs_mpage_readpages() calls f2fs_read_multi_pages() when nr_pages=1, at
> that time, max_nr_pages equals to 1 as well.
> 
> f2fs_grab_read_bio(..., 1 - 0,...) allocate bio w/ 1 vec capacity, however,
> we need at least 3 vecs to merge all cpages, right?
> 

Hi, chao,

If we don't align nr_pages, then when entering f2fs_read_multi_pages,
we have nr_pages pages left, which belong to other clusters.
If this is the last page, we can simply pass nr_pages = 0.

When allocating bio, we need:
1. The cpages remaining in the current cluster, which should be 
(nr_capges - i).
2. The maximum cpages remaining in other clusters, which should be 
max(nr_pages, cc->nr_cpages).

So (nr_capges - i) + max(nr_pages, nr_cpages), should be enough for all 
vecs?

Thanks,


> Thanks,
> 
>>                                        f2fs_ra_op_flags(rac),
>>                                        folio->index, for_write);
>>                        if (IS_ERR(bio)) {
>> @@ -2376,6 +2376,14 @@ static int f2fs_mpage_readpages(struct inode *inode,
>>        unsigned max_nr_pages = nr_pages;
>>        int ret = 0;
>>
>> +#ifdef CONFIG_F2FS_FS_COMPRESSION
>> +     if (f2fs_compressed_file(inode)) {
>> +             index = rac ? readahead_index(rac) : folio->index;
>> +             max_nr_pages = round_up(index + nr_pages, cc.cluster_size) -
>> +                             round_down(index, cc.cluster_size);
>> +     }
>> +#endif
>> +
>>        map.m_pblk = 0;
>>        map.m_lblk = 0;
>>        map.m_len = 0;
>> @@ -2385,7 +2393,7 @@ static int f2fs_mpage_readpages(struct inode *inode,
>>        map.m_seg_type = NO_CHECK_TYPE;
>>        map.m_may_create = false;
>>
>> -     for (; nr_pages; nr_pages--) {
>> +     for (; nr_pages; nr_pages--, max_nr_pages--) {
>>                if (rac) {
>>                        folio = readahead_folio(rac);
>>                        prefetchw(&folio->flags);
> 

Re: [External Mail]Re: [PATCH v3] f2fs: avoid splitting bio when reading multiple pages

[Huang Jianan]

On 2025/6/25 17:48, Jianan Huang wrote:
> On 2025/6/25 16:45, Chao Yu wrote:
>>
>> On 6/25/25 14:49, Jianan Huang wrote:
>>> When fewer pages are read, nr_pages may be smaller than nr_cpages. Due
>>> to the nr_vecs limit, the compressed pages will be split into multiple
>>> bios and then merged at the block level. In this case, nr_cpages should
>>> be used to pre-allocate bvecs.
>>> To handle this case, align max_nr_pages to cluster_size, which should be
>>> enough for all compressed pages.
>>>
>>> Signed-off-by: Jianan Huang <huangjianan@xiaomi.com>
>>> Signed-off-by: Sheng Yong <shengyong1@xiaomi.com>
>>> ---
>>> Changes since v2:
>>> - Initialize index only for compressed files.
>>> Changes since v1:
>>> - Use aligned nr_pages instead of nr_cpages to pre-allocate bvecs.
>>>
>>>   fs/f2fs/data.c | 12 ++++++++++--
>>>   1 file changed, 10 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
>>> index 31e892842625..d071d9f6a811 100644
>>> --- a/fs/f2fs/data.c
>>> +++ b/fs/f2fs/data.c
>>> @@ -2303,7 +2303,7 @@ int f2fs_read_multi_pages(struct compress_ctx 
>>> *cc, struct bio **bio_ret,
>>>                }
>>>
>>>                if (!bio) {
>>> -                     bio = f2fs_grab_read_bio(inode, blkaddr, nr_pages,
>>> +                     bio = f2fs_grab_read_bio(inode, blkaddr, 
>>> nr_pages - i,
>>
>> Jianan,
>>
>> Another case:
>>
>> read page #0,1,2,3 from block #1000,1001,1002, cluster_size=4.
>>
>> nr_pages=4
>> max_nr_pages=round_up(0+4,4)-round_down(0,4)=4
>>
>> f2fs_mpage_readpages() calls f2fs_read_multi_pages() when nr_pages=1, at
>> that time, max_nr_pages equals to 1 as well.
>>
>> f2fs_grab_read_bio(..., 1 - 0,...) allocate bio w/ 1 vec capacity, 
>> however,
>> we need at least 3 vecs to merge all cpages, right?
>>
> 
> Hi, chao,
> 
> If we don't align nr_pages, then when entering f2fs_read_multi_pages,
> we have nr_pages pages left, which belong to other clusters.
> If this is the last page, we can simply pass nr_pages = 0.
> 
> When allocating bio, we need:
> 1. The cpages remaining in the current cluster, which should be 
> (nr_capges - i).
> 2. The maximum cpages remaining in other clusters, which should be 
> max(nr_pages, cc->nr_cpages).
> 

align(nr_pages, cc->nr_cpages), sorry for this.

> So (nr_capges - i) + max(nr_pages, nr_cpages), should be enough for all 
> vecs?
> 
> Thanks,
> 
> 
>> Thanks,
>>
>>>                                        f2fs_ra_op_flags(rac),
>>>                                        folio->index, for_write);
>>>                        if (IS_ERR(bio)) {
>>> @@ -2376,6 +2376,14 @@ static int f2fs_mpage_readpages(struct inode 
>>> *inode,
>>>        unsigned max_nr_pages = nr_pages;
>>>        int ret = 0;
>>>
>>> +#ifdef CONFIG_F2FS_FS_COMPRESSION
>>> +     if (f2fs_compressed_file(inode)) {
>>> +             index = rac ? readahead_index(rac) : folio->index;
>>> +             max_nr_pages = round_up(index + nr_pages, 
>>> cc.cluster_size) -
>>> +                             round_down(index, cc.cluster_size);
>>> +     }
>>> +#endif
>>> +
>>>        map.m_pblk = 0;
>>>        map.m_lblk = 0;
>>>        map.m_len = 0;
>>> @@ -2385,7 +2393,7 @@ static int f2fs_mpage_readpages(struct inode 
>>> *inode,
>>>        map.m_seg_type = NO_CHECK_TYPE;
>>>        map.m_may_create = false;
>>>
>>> -     for (; nr_pages; nr_pages--) {
>>> +     for (; nr_pages; nr_pages--, max_nr_pages--) {
>>>                if (rac) {
>>>                        folio = readahead_folio(rac);
>>>                        prefetchw(&folio->flags);
>>
> 

Re: [External Mail]Re: [PATCH v3] f2fs: avoid splitting bio when reading multiple pages

[Chao Yu]

On 6/25/25 17:50, Huang Jianan wrote:
> On 2025/6/25 17:48, Jianan Huang wrote:
>> On 2025/6/25 16:45, Chao Yu wrote:
>>>
>>> On 6/25/25 14:49, Jianan Huang wrote:
>>>> When fewer pages are read, nr_pages may be smaller than nr_cpages. Due
>>>> to the nr_vecs limit, the compressed pages will be split into multiple
>>>> bios and then merged at the block level. In this case, nr_cpages should
>>>> be used to pre-allocate bvecs.
>>>> To handle this case, align max_nr_pages to cluster_size, which should be
>>>> enough for all compressed pages.
>>>>
>>>> Signed-off-by: Jianan Huang <huangjianan@xiaomi.com>
>>>> Signed-off-by: Sheng Yong <shengyong1@xiaomi.com>
>>>> ---
>>>> Changes since v2:
>>>> - Initialize index only for compressed files.
>>>> Changes since v1:
>>>> - Use aligned nr_pages instead of nr_cpages to pre-allocate bvecs.
>>>>
>>>>   fs/f2fs/data.c | 12 ++++++++++--
>>>>   1 file changed, 10 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
>>>> index 31e892842625..d071d9f6a811 100644
>>>> --- a/fs/f2fs/data.c
>>>> +++ b/fs/f2fs/data.c
>>>> @@ -2303,7 +2303,7 @@ int f2fs_read_multi_pages(struct compress_ctx 
>>>> *cc, struct bio **bio_ret,
>>>>                }
>>>>
>>>>                if (!bio) {
>>>> -                     bio = f2fs_grab_read_bio(inode, blkaddr, nr_pages,
>>>> +                     bio = f2fs_grab_read_bio(inode, blkaddr, 
>>>> nr_pages - i,
>>>
>>> Jianan,
>>>
>>> Another case:
>>>
>>> read page #0,1,2,3 from block #1000,1001,1002, cluster_size=4.
>>>
>>> nr_pages=4
>>> max_nr_pages=round_up(0+4,4)-round_down(0,4)=4
>>>
>>> f2fs_mpage_readpages() calls f2fs_read_multi_pages() when nr_pages=1, at
>>> that time, max_nr_pages equals to 1 as well.
>>>
>>> f2fs_grab_read_bio(..., 1 - 0,...) allocate bio w/ 1 vec capacity, 
>>> however,
>>> we need at least 3 vecs to merge all cpages, right?
>>>
>>
>> Hi, chao,
>>
>> If we don't align nr_pages, then when entering f2fs_read_multi_pages,
>> we have nr_pages pages left, which belong to other clusters.
>> If this is the last page, we can simply pass nr_pages = 0.
>>
>> When allocating bio, we need:
>> 1. The cpages remaining in the current cluster, which should be 
>> (nr_capges - i).
>> 2. The maximum cpages remaining in other clusters, which should be 
>> max(nr_pages, cc->nr_cpages).
>>
> 
> align(nr_pages, cc->nr_cpages), sorry for this.
> 
>> So (nr_capges - i) + max(nr_pages, nr_cpages), should be enough for all 
>> vecs?

Jianan,

What about getting rid of below change? and just passing max_nr_pages to
f2fs_read_multi_pages? Maybe there is a little bit waste for bio vector space,
but it will be more safe to reserve enough margin.

+	for (; nr_pages; nr_pages--, max_nr_pages--) {

Thanks,

>>
>> Thanks,
>>
>>
>>> Thanks,
>>>
>>>>                                        f2fs_ra_op_flags(rac),
>>>>                                        folio->index, for_write);
>>>>                        if (IS_ERR(bio)) {
>>>> @@ -2376,6 +2376,14 @@ static int f2fs_mpage_readpages(struct inode 
>>>> *inode,
>>>>        unsigned max_nr_pages = nr_pages;
>>>>        int ret = 0;
>>>>
>>>> +#ifdef CONFIG_F2FS_FS_COMPRESSION
>>>> +     if (f2fs_compressed_file(inode)) {
>>>> +             index = rac ? readahead_index(rac) : folio->index;
>>>> +             max_nr_pages = round_up(index + nr_pages, 
>>>> cc.cluster_size) -
>>>> +                             round_down(index, cc.cluster_size);
>>>> +     }
>>>> +#endif
>>>> +
>>>>        map.m_pblk = 0;
>>>>        map.m_lblk = 0;
>>>>        map.m_len = 0;
>>>> @@ -2385,7 +2393,7 @@ static int f2fs_mpage_readpages(struct inode 
>>>> *inode,
>>>>        map.m_seg_type = NO_CHECK_TYPE;
>>>>        map.m_may_create = false;
>>>>
>>>> -     for (; nr_pages; nr_pages--) {
>>>> +     for (; nr_pages; nr_pages--, max_nr_pages--) {
>>>>                if (rac) {
>>>>                        folio = readahead_folio(rac);
>>>>                        prefetchw(&folio->flags);
>>>
>>
> 

Re: [External Mail]Re: [PATCH v3] f2fs: avoid splitting bio when reading multiple pages

[Huang Jianan]

On 2025/6/30 19:23, Chao Yu wrote:
> 
> On 6/25/25 17:50, Huang Jianan wrote:
>> On 2025/6/25 17:48, Jianan Huang wrote:
>>> On 2025/6/25 16:45, Chao Yu wrote:
>>>>
>>>> On 6/25/25 14:49, Jianan Huang wrote:
>>>>> When fewer pages are read, nr_pages may be smaller than nr_cpages. Due
>>>>> to the nr_vecs limit, the compressed pages will be split into multiple
>>>>> bios and then merged at the block level. In this case, nr_cpages should
>>>>> be used to pre-allocate bvecs.
>>>>> To handle this case, align max_nr_pages to cluster_size, which should be
>>>>> enough for all compressed pages.
>>>>>
>>>>> Signed-off-by: Jianan Huang <huangjianan@xiaomi.com>
>>>>> Signed-off-by: Sheng Yong <shengyong1@xiaomi.com>
>>>>> ---
>>>>> Changes since v2:
>>>>> - Initialize index only for compressed files.
>>>>> Changes since v1:
>>>>> - Use aligned nr_pages instead of nr_cpages to pre-allocate bvecs.
>>>>>
>>>>>    fs/f2fs/data.c | 12 ++++++++++--
>>>>>    1 file changed, 10 insertions(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
>>>>> index 31e892842625..d071d9f6a811 100644
>>>>> --- a/fs/f2fs/data.c
>>>>> +++ b/fs/f2fs/data.c
>>>>> @@ -2303,7 +2303,7 @@ int f2fs_read_multi_pages(struct compress_ctx
>>>>> *cc, struct bio **bio_ret,
>>>>>                 }
>>>>>
>>>>>                 if (!bio) {
>>>>> -                     bio = f2fs_grab_read_bio(inode, blkaddr, nr_pages,
>>>>> +                     bio = f2fs_grab_read_bio(inode, blkaddr,
>>>>> nr_pages - i,
>>>>
>>>> Jianan,
>>>>
>>>> Another case:
>>>>
>>>> read page #0,1,2,3 from block #1000,1001,1002, cluster_size=4.
>>>>
>>>> nr_pages=4
>>>> max_nr_pages=round_up(0+4,4)-round_down(0,4)=4
>>>>
>>>> f2fs_mpage_readpages() calls f2fs_read_multi_pages() when nr_pages=1, at
>>>> that time, max_nr_pages equals to 1 as well.
>>>>
>>>> f2fs_grab_read_bio(..., 1 - 0,...) allocate bio w/ 1 vec capacity,
>>>> however,
>>>> we need at least 3 vecs to merge all cpages, right?
>>>>
>>>
>>> Hi, chao,
>>>
>>> If we don't align nr_pages, then when entering f2fs_read_multi_pages,
>>> we have nr_pages pages left, which belong to other clusters.
>>> If this is the last page, we can simply pass nr_pages = 0.
>>>
>>> When allocating bio, we need:
>>> 1. The cpages remaining in the current cluster, which should be
>>> (nr_capges - i).
>>> 2. The maximum cpages remaining in other clusters, which should be
>>> max(nr_pages, cc->nr_cpages).
>>>
>>
>> align(nr_pages, cc->nr_cpages), sorry for this.
>>
>>> So (nr_capges - i) + max(nr_pages, nr_cpages), should be enough for all
>>> vecs?
> 
> Jianan,
> 
> What about getting rid of below change? and just passing max_nr_pages to
> f2fs_read_multi_pages? Maybe there is a little bit waste for bio vector space,
> but it will be more safe to reserve enough margin.
> 
> +       for (; nr_pages; nr_pages--, max_nr_pages--) {
> 

LGTM, updated in v4.

Thanks,

> Thanks,
> 
>>>
>>> Thanks,
>>>
>>>
>>>> Thanks,
>>>>
>>>>>                                         f2fs_ra_op_flags(rac),
>>>>>                                         folio->index, for_write);
>>>>>                         if (IS_ERR(bio)) {
>>>>> @@ -2376,6 +2376,14 @@ static int f2fs_mpage_readpages(struct inode
>>>>> *inode,
>>>>>         unsigned max_nr_pages = nr_pages;
>>>>>         int ret = 0;
>>>>>
>>>>> +#ifdef CONFIG_F2FS_FS_COMPRESSION
>>>>> +     if (f2fs_compressed_file(inode)) {
>>>>> +             index = rac ? readahead_index(rac) : folio->index;
>>>>> +             max_nr_pages = round_up(index + nr_pages,
>>>>> cc.cluster_size) -
>>>>> +                             round_down(index, cc.cluster_size);
>>>>> +     }
>>>>> +#endif
>>>>> +
>>>>>         map.m_pblk = 0;
>>>>>         map.m_lblk = 0;
>>>>>         map.m_len = 0;
>>>>> @@ -2385,7 +2393,7 @@ static int f2fs_mpage_readpages(struct inode
>>>>> *inode,
>>>>>         map.m_seg_type = NO_CHECK_TYPE;
>>>>>         map.m_may_create = false;
>>>>>
>>>>> -     for (; nr_pages; nr_pages--) {
>>>>> +     for (; nr_pages; nr_pages--, max_nr_pages--) {
>>>>>                 if (rac) {
>>>>>                         folio = readahead_folio(rac);
>>>>>                         prefetchw(&folio->flags);
>>>>
>>>
>>
>