| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <2a12d76e-6458-4626-b761-558c143aa289@linux.alibaba.com>
Date: Fri, 18 Oct 2024 09:45:01 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Yang Shi <shy828301@...il.com>
Cc: Matthew Wilcox <willy@...radead.org>, akpm@...ux-foundation.org,
hughd@...gle.com, david@...hat.com, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] mm: shmem: improve the tmpfs large folio read
performance
On 2024/10/18 00:48, Yang Shi wrote:
> On Wed, Oct 16, 2024 at 8:25 PM Baolin Wang
> <baolin.wang@...ux.alibaba.com> wrote:
>>
>>
>>
>> On 2024/10/17 01:33, Yang Shi wrote:
>>> On Wed, Oct 16, 2024 at 8:38 AM Matthew Wilcox <willy@...radead.org> wrote:
>>>>
>>>> On Wed, Oct 16, 2024 at 06:09:30PM +0800, Baolin Wang wrote:
>>>>> @@ -3128,8 +3127,9 @@ static ssize_t shmem_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
>>>>> if (folio) {
>>>>> folio_unlock(folio);
>>>>>
>>>>> - page = folio_file_page(folio, index);
>>>>> - if (PageHWPoison(page)) {
>>>>> + if (folio_test_hwpoison(folio) ||
>>>>> + (folio_test_large(folio) &&
>>>>> + folio_test_has_hwpoisoned(folio))) {
>>>>
>>>> Hm, so if we have hwpoison set on one page in a folio, we now can't read
>>>> bytes from any page in the folio? That seems like we've made a bad
>>>> situation worse.
>>>
>>> Yeah, I agree. I think we can fallback to page copy if
>>> folio_test_has_hwpoisoned is true. The PG_hwpoison flag is per page.
>>>
>>> The folio_test_has_hwpoisoned is kept set if the folio split is failed
>>> in memory failure handler.
>>
>> Right. I can still keep the page size copy if
>> folio_test_has_hwpoisoned() is true. Some sample changes are as follow.
>>
>> Moreover, I noticed shmem splice_read() and write() also simply return
>> an error if the folio_test_has_hwpoisoned() is true, without any
>> fallback to page granularity. I wonder if it is worth adding page
>> granularity support as well?
>
> I think you should do the same.
OK. Let me have a detailed look.
>> diff --git a/mm/shmem.c b/mm/shmem.c
>> index 7e79b6a96da0..f30e24e529b9 100644
>> --- a/mm/shmem.c
>> +++ b/mm/shmem.c
>> @@ -3111,9 +3111,11 @@ static ssize_t shmem_file_read_iter(struct kiocb
>> *iocb, struct iov_iter *to)
>>
>> for (;;) {
>> struct folio *folio = NULL;
>> + struct page *page = NULL;
>> unsigned long nr, ret;
>> loff_t end_offset, i_size = i_size_read(inode);
>> size_t fsize;
>> + bool fallback_page_copy = false;
>>
>> if (unlikely(iocb->ki_pos >= i_size))
>> break;
>> @@ -3127,13 +3129,16 @@ static ssize_t shmem_file_read_iter(struct kiocb
>> *iocb, struct iov_iter *to)
>> if (folio) {
>> folio_unlock(folio);
>>
>> - if (folio_test_hwpoison(folio) ||
>> - (folio_test_large(folio) &&
>> - folio_test_has_hwpoisoned(folio))) {
>> + page = folio_file_page(folio, index);
>> + if (PageHWPoison(page)) {
>> folio_put(folio);
>> error = -EIO;
>> break;
>> }
>> +
>> + if (folio_test_large(folio) &&
>> + folio_test_has_hwpoisoned(folio))
>> + fallback_page_copy = true;
>> }
>>
>> /*
>> @@ -3147,7 +3152,7 @@ static ssize_t shmem_file_read_iter(struct kiocb
>> *iocb, struct iov_iter *to)
>> break;
>> }
>> end_offset = min_t(loff_t, i_size, iocb->ki_pos +
>> to->count);
>> - if (folio)
>> + if (folio && likely(!fallback_page_copy))
>> fsize = folio_size(folio);
>> else
>> fsize = PAGE_SIZE;
>> @@ -3160,8 +3165,13 @@ static ssize_t shmem_file_read_iter(struct kiocb
>> *iocb, struct iov_iter *to)
>> * virtual addresses, take care about potential
>> aliasing
>> * before reading the page on the kernel side.
>> */
>> - if (mapping_writably_mapped(mapping))
>> - flush_dcache_folio(folio);
>> + if (mapping_writably_mapped(mapping)) {
>> + if (unlikely(fallback_page_copy))
>> + flush_dcache_page(page);
>> + else
>> + flush_dcache_folio(folio);
>> + }
>> +
>> /*
>> * Mark the page accessed if we read the beginning.
>> */
>> @@ -3171,7 +3181,10 @@ static ssize_t shmem_file_read_iter(struct kiocb
>> *iocb, struct iov_iter *to)
>> * Ok, we have the page, and it's up-to-date, so
>> * now we can copy it to user space...
>> */
>> - ret = copy_folio_to_iter(folio, offset, nr, to);
>> + if (unlikely(fallback_page_copy))
>> + ret = copy_page_to_iter(page, offset,
>> nr, to);
>> + else
>> + ret = copy_folio_to_iter(folio, offset,
>> nr, to);
>> folio_put(folio);
>> } else if (user_backed_iter(to)) {
>> /*
>
> The change seems fine to me.
Thanks.
Powered by blists - more mailing lists