| 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: <c7c3f529-4cd0-4209-b3b9-48a29dfcb08d@redhat.com>
Date: Tue, 12 Nov 2024 17:19:32 +0100
From: David Hildenbrand <david@...hat.com>
To: Baolin Wang <baolin.wang@...ux.alibaba.com>, akpm@...ux-foundation.org,
hughd@...gle.com
Cc: willy@...radead.org, wangkefeng.wang@...wei.com, 21cnbao@...il.com,
ryan.roberts@....com, ioworker0@...il.com, da.gomez@...sung.com,
linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/5] mm: shmem: add large folio support for tmpfs
On 12.11.24 08:45, Baolin Wang wrote:
> Add large folio support for tmpfs write and fallocate paths matching the
> same high order preference mechanism used in the iomap buffered IO path
> as used in __filemap_get_folio().
>
> Add shmem_mapping_size_orders() to get a hint for the orders of the folio
> based on the file size which takes care of the mapping requirements.
>
> Traditionally, tmpfs only supported PMD-sized huge folios. However nowadays
> with other file systems supporting any sized large folios, and extending
> anonymous to support mTHP, we should not restrict tmpfs to allocating only
> PMD-sized huge folios, making it more special. Instead, we should allow
> tmpfs can allocate any sized large folios.
>
> Considering that tmpfs already has the 'huge=' option to control the huge
> folios allocation, we can extend the 'huge=' option to allow any sized huge
> folios. The semantics of the 'huge=' mount option are:
>
> huge=never: no any sized huge folios
> huge=always: any sized huge folios
> huge=within_size: like 'always' but respect the i_size
> huge=advise: like 'always' if requested with fadvise()/madvise()
>
> Note: for tmpfs mmap() faults, due to the lack of a write size hint, still
> allocate the PMD-sized huge folios if huge=always/within_size/advise is set.
>
> Moreover, the 'deny' and 'force' testing options controlled by
> '/sys/kernel/mm/transparent_hugepage/shmem_enabled', still retain the same
> semantics. The 'deny' can disable any sized large folios for tmpfs, while
> the 'force' can enable PMD sized large folios for tmpfs.
>
> Co-developed-by: Daniel Gomez <da.gomez@...sung.com>
> Signed-off-by: Daniel Gomez <da.gomez@...sung.com>
> Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> ---
> mm/shmem.c | 91 +++++++++++++++++++++++++++++++++++++++++++++---------
> 1 file changed, 77 insertions(+), 14 deletions(-)
>
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 86b2e417dc6f..a3203cf8860f 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -549,10 +549,50 @@ static bool shmem_confirm_swap(struct address_space *mapping,
>
> static int shmem_huge __read_mostly = SHMEM_HUGE_NEVER;
>
> +/**
> + * shmem_mapping_size_orders - Get allowable folio orders for the given file size.
> + * @mapping: Target address_space.
> + * @index: The page index.
> + * @write_end: end of a write, could extend inode size.
> + *
> + * This returns huge orders for folios (when supported) based on the file size
> + * which the mapping currently allows at the given index. The index is relevant
> + * due to alignment considerations the mapping might have. The returned order
> + * may be less than the size passed.
> + *
> + * Return: The orders.
> + */
> +static inline unsigned int
> +shmem_mapping_size_orders(struct address_space *mapping, pgoff_t index, loff_t write_end)
> +{
> + unsigned int order;
> + size_t size;
> +
> + if (!mapping_large_folio_support(mapping) || !write_end)
> + return 0;
> +
> + /* Calculate the write size based on the write_end */
> + size = write_end - (index << PAGE_SHIFT);
> + order = filemap_get_order(size);
> + if (!order)
> + return 0;
> +
> + /* If we're not aligned, allocate a smaller folio */
> + if (index & ((1UL << order) - 1))
> + order = __ffs(index);
> +
> + order = min_t(size_t, order, MAX_PAGECACHE_ORDER);
> + return order > 0 ? BIT(order + 1) - 1 : 0;
> +}
> +
> static unsigned int shmem_huge_global_enabled(struct inode *inode, pgoff_t index,
> loff_t write_end, bool shmem_huge_force,
> + struct vm_area_struct *vma,
> unsigned long vm_flags)
> {
> + unsigned long within_size_orders;
> + unsigned int order;
> + pgoff_t aligned_index;
> loff_t i_size;
>
> if (HPAGE_PMD_ORDER > MAX_PAGECACHE_ORDER)
We can allow all orders up to MAX_PAGECACHE_ORDER,
shmem_mapping_size_orders() handles it properly.
So maybe we should drop this condition and use instead below where we have
return BIT(HPAGE_PMD_ORDER);
instead something like.
return HPAGE_PMD_ORDER > MAX_PAGECACHE_ORDER ? 0 : BIT(HPAGE_PMD_ORDER);
Ideally, factoring it out somehow
int maybe_pmd_order = HPAGE_PMD_ORDER > MAX_PAGECACHE_ORDER ? 0 :
BIT(HPAGE_PMD_ORDER);
...
return maybe_pmd_order;
> @@ -564,15 +604,41 @@ static unsigned int shmem_huge_global_enabled(struct inode *inode, pgoff_t index
> if (shmem_huge_force || shmem_huge == SHMEM_HUGE_FORCE)
> return BIT(HPAGE_PMD_ORDER);
Why not force-enable all orders (of course, respecting
MAX_PAGECACHE_ORDER and possibly VMA)?
>
> + /*
> + * The huge order allocation for anon shmem is controlled through
> + * the mTHP interface, so we still use PMD-sized huge order to
> + * check whether global control is enabled.
> + *
> + * For tmpfs mmap()'s huge order, we still use PMD-sized order to
> + * allocate huge pages due to lack of a write size hint.
> + *
> + * Otherwise, tmpfs will allow getting a highest order hint based on
> + * the size of write and fallocate paths, then will try each allowable
> + * huge orders.
> + */
> switch (SHMEM_SB(inode->i_sb)->huge) {
> case SHMEM_HUGE_ALWAYS:
> - return BIT(HPAGE_PMD_ORDER);
> - case SHMEM_HUGE_WITHIN_SIZE:
> - index = round_up(index + 1, HPAGE_PMD_NR);
> - i_size = max(write_end, i_size_read(inode));
> - i_size = round_up(i_size, PAGE_SIZE);
> - if (i_size >> PAGE_SHIFT >= index)
> + if (vma)
> return BIT(HPAGE_PMD_ORDER);
> +
> + return shmem_mapping_size_orders(inode->i_mapping, index, write_end);
> + case SHMEM_HUGE_WITHIN_SIZE:
> + if (vma)
> + within_size_orders = BIT(HPAGE_PMD_ORDER);
> + else
> + within_size_orders = shmem_mapping_size_orders(inode->i_mapping,
> + index, write_end);
> +
> + order = highest_order(within_size_orders);
> + while (within_size_orders) {
> + aligned_index = round_up(index + 1, 1 << order);
> + i_size = max(write_end, i_size_read(inode));
> + i_size = round_up(i_size, PAGE_SIZE);
> + if (i_size >> PAGE_SHIFT >= aligned_index)
> + return within_size_orders;
> +
> + order = next_order(&within_size_orders, order);
> + }
> fallthrough;
> case SHMEM_HUGE_ADVISE:
> if (vm_flags & VM_HUGEPAGE)
I think the point here is that "write" -> no VMA -> vm_flags == 0 -> no
code changes needed :)
--
Cheers,
David / dhildenb
Powered by blists - more mailing lists