Re: [PATCH 2/2] mm/hugetlb: add wrapper functions for interactions with page cache
From: Mike Kravetz
Date: Thu Jun 15 2023 - 19:37:13 EST
On 06/09/23 12:52, Sidhartha Kumar wrote:
> On 6/9/23 12:49 PM, Sidhartha Kumar wrote:
> > Signed-off-by: Sidhartha Kumar <sidhartha.kumar@xxxxxxxxxx>
>
> Sorry, I missed adding the commit message to this. It should be:
>
> Add filemap_lock_hugetlb_folio() which is wraps __filemap_get_folio()
> and passes in a linear page index. hugetlb_add_to_page_cache() is modified
> to also compute a linear page index before calling into page cache code.
>
> linear_page_index() is modified to perform the computation on hugetlb
> so we can use it in the page cache wrappers.
>
> > ---
> > fs/hugetlbfs/inode.c | 14 +++++++-------
> > include/linux/hugetlb.h | 21 +++++++++++++++++++--
> > include/linux/pagemap.h | 2 --
> > mm/hugetlb.c | 22 +++++++++++++---------
> > 4 files changed, 39 insertions(+), 20 deletions(-)
> >
> > diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
> > index 90361a922cec7..90d27a8af4b6a 100644
> > --- a/fs/hugetlbfs/inode.c
> > +++ b/fs/hugetlbfs/inode.c
> > @@ -617,20 +617,19 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart,
> > struct hstate *h = hstate_inode(inode);
> > struct address_space *mapping = &inode->i_data;
> > const pgoff_t start = lstart >> huge_page_shift(h);
> > - const pgoff_t end = lend >> huge_page_shift(h);
> > struct folio_batch fbatch;
> > pgoff_t next, index;
> > int i, freed = 0;
> > bool truncate_op = (lend == LLONG_MAX);
> > folio_batch_init(&fbatch);
> > - next = start;
> > - while (filemap_get_folios(mapping, &next, end - 1, &fbatch)) {
> > + next = lstart;
> > + while (filemap_get_folios(mapping, &next, lend - 1, &fbatch)) {
This does not seem correct. At this point next == lstart which is a file
offset passed to the routine as opposed to an index.
I would think next needs to be set to 'lstart >> PAGE_SHIFT' here.
> > for (i = 0; i < folio_batch_count(&fbatch); ++i) {
> > struct folio *folio = fbatch.folios[i];
> > u32 hash = 0;
> > - index = folio->index;
> > + index = (folio->index) >> huge_page_shift(h);
Here you want to convert index from the PAGE_SIZE index to a hugetlb
page size index. Correct?
I am terrible at arithmetic, but huge_page_shift already includes
PAGE_SHIFT, so it seems like you want this to me.
index = (folio->index) >> huge_page_order(h);
> > hash = hugetlb_fault_mutex_hash(mapping, index);
> > mutex_lock(&hugetlb_fault_mutex_table[hash]);
> > @@ -693,10 +692,11 @@ static void hugetlbfs_zero_partial_page(struct hstate *h,
> > loff_t start,
> > loff_t end)
> > {
> > - pgoff_t idx = start >> huge_page_shift(h);
> > + struct mm_struct *mm = current->mm;
> > + struct vm_area_struct *vma = find_vma(mm, start);
> > struct folio *folio;
> > - folio = filemap_lock_folio(mapping, idx);
> > + folio = filemap_lock_hugetlb_folio(vma, start);
Here you are passing an address/index that may be associated with a
tail page. I assume since the hugetlb folio is multi-order, the
returned folio will be for the 'head page'. Correct?
> > if (IS_ERR(folio))
> > return;
> > @@ -868,7 +868,7 @@ static long hugetlbfs_fallocate(struct file *file, int mode, loff_t offset,
> > }
> > clear_huge_page(&folio->page, addr, pages_per_huge_page(h));
> > __folio_mark_uptodate(folio);
> > - error = hugetlb_add_to_page_cache(folio, mapping, index);
> > + error = hugetlb_add_to_page_cache(folio, &pseudo_vma, mapping, addr);
> > if (unlikely(error)) {
> > restore_reserve_on_error(h, &pseudo_vma, addr, folio);
> > folio_put(folio);
> > diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> > index 21f942025fecd..55f90e051b7a2 100644
> > --- a/include/linux/hugetlb.h
> > +++ b/include/linux/hugetlb.h
> > @@ -727,8 +727,8 @@ struct folio *alloc_hugetlb_folio_nodemask(struct hstate *h, int preferred_nid,
> > nodemask_t *nmask, gfp_t gfp_mask);
> > struct folio *alloc_hugetlb_folio_vma(struct hstate *h, struct vm_area_struct *vma,
> > unsigned long address);
> > -int hugetlb_add_to_page_cache(struct folio *folio, struct address_space *mapping,
> > - pgoff_t idx);
> > +int hugetlb_add_to_page_cache(struct folio *folio, struct vm_area_struct *vma,
> > + struct address_space *mapping, unsigned long address);
> > void restore_reserve_on_error(struct hstate *h, struct vm_area_struct *vma,
> > unsigned long address, struct folio *folio);
> > @@ -755,6 +755,16 @@ static inline struct hugepage_subpool *hugetlb_folio_subpool(struct folio *folio
> > return folio->_hugetlb_subpool;
> > }
> > +/* Wrapper function for __filemap_get_folio*/
> > +static inline struct folio *filemap_lock_hugetlb_folio(struct vm_area_struct *vma,
> > + unsigned long address)
> > +{
> > + struct address_space *mapping = vma->vm_file->f_mapping;
> > +
> > + pgoff_t idx = linear_page_index(vma, address);
> > + return __filemap_get_folio(mapping, idx, FGP_LOCK, 0);
> > +}
I like the wrapper idea. This is going to replace existing calls to
filemap_lock_folio. What about something like this for the routine:
static inline struct folio *filemap_lock_hugetlb_folio(struct hstate *h,
struct address_space *mapping,
pgoff_t index);
{
/* please verify my arithmetic */
return filemap_lock_folio(mapping, index << huge_page_order(h));
}
In this way, existing callers would only need to be changed to pass in
hstate. Perhaps, there was a reason for your wrapper not obvious to me?
> > +
> > static inline void hugetlb_set_folio_subpool(struct folio *folio,
> > struct hugepage_subpool *subpool)
> > {
> > @@ -1021,6 +1031,13 @@ static inline struct hugepage_subpool *hugetlb_folio_subpool(struct folio *folio
> > return NULL;
> > }
> > +/* Wrapper function for __filemap_get_folio*/
> > +static inline struct folio *filemap_lock_hugetlb_folio(struct vm_area_struct *vma,
> > + unsigned long address)
> > +{
> > + return NULL;
> > +}
> > +
> > static inline int isolate_or_dissolve_huge_page(struct page *page,
> > struct list_head *list)
> > {
> > diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> > index 17c414fc2136e..ae8f36966d7b3 100644
> > --- a/include/linux/pagemap.h
> > +++ b/include/linux/pagemap.h
> > @@ -860,8 +860,6 @@ static inline pgoff_t linear_page_index(struct vm_area_struct *vma,
> > unsigned long address)
> > {
> > pgoff_t pgoff;
> > - if (unlikely(is_vm_hugetlb_page(vma)))
> > - return linear_hugepage_index(vma, address);
> > pgoff = (address - vma->vm_start) >> PAGE_SHIFT;
> > pgoff += vma->vm_pgoff;
> > return pgoff;
> > diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> > index dfa412d8cb300..824d6d215a161 100644
> > --- a/mm/hugetlb.c
> > +++ b/mm/hugetlb.c
> > @@ -951,7 +951,7 @@ static long region_count(struct resv_map *resv, long f, long t)
> > /*
> > * Convert the address within this vma to the page offset within
> > - * the mapping, in pagecache page units; huge pages here.
> > + * the mapping, in huge page units here.
> > */
> > static pgoff_t vma_hugecache_offset(struct hstate *h,
> > struct vm_area_struct *vma, unsigned long address)
> > @@ -5730,7 +5730,7 @@ static bool hugetlbfs_pagecache_present(struct hstate *h,
> > struct vm_area_struct *vma, unsigned long address)
> > {
> > struct address_space *mapping = vma->vm_file->f_mapping;
> > - pgoff_t idx = vma_hugecache_offset(h, vma, address);
> > + pgoff_t idx = linear_page_index(vma, address);
> > bool present;
> > rcu_read_lock();
> > @@ -5740,13 +5740,16 @@ static bool hugetlbfs_pagecache_present(struct hstate *h,
> > return present;
> > }
> > -int hugetlb_add_to_page_cache(struct folio *folio, struct address_space *mapping,
> > - pgoff_t idx)
> > +int hugetlb_add_to_page_cache(struct folio *folio,
> > + struct vm_area_struct *vma,
> > + struct address_space *mapping,
> > + unsigned long address)
> > {
Like filemap_lock_hugetlb_folio(), can you just add hstate to existing
hugetlb_add_to_page_cache() arguments and do arithmetic to convert index
to PAGE_SIZE based index?
Again, I could be missing something. But, IMO such a conversion would
minimize changes to the current code.
--
Mike Kravetz
> > struct inode *inode = mapping->host;
> > struct hstate *h = hstate_inode(inode);
> > int err;
> > + pgoff_t idx = linear_page_index(vma, address);
> > __folio_set_locked(folio);
> > err = __filemap_add_folio(mapping, folio, idx, GFP_KERNEL, NULL);
> > @@ -5854,7 +5857,8 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm,
> > * before we get page_table_lock.
> > */
> > new_folio = false;
> > - folio = filemap_lock_folio(mapping, idx);
> > +
> > + folio = filemap_lock_hugetlb_folio(vma, address);
> > if (IS_ERR(folio)) {
> > size = i_size_read(mapping->host) >> huge_page_shift(h);
> > if (idx >= size)
> > @@ -5913,7 +5917,7 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm,
> > new_folio = true;
> > if (vma->vm_flags & VM_MAYSHARE) {
> > - int err = hugetlb_add_to_page_cache(folio, mapping, idx);
> > + int err = hugetlb_add_to_page_cache(folio, vma, mapping, address);
> > if (err) {
> > /*
> > * err can't be -EEXIST which implies someone
> > @@ -6145,7 +6149,7 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
> > /* Just decrements count, does not deallocate */
> > vma_end_reservation(h, vma, haddr);
> > - pagecache_folio = filemap_lock_folio(mapping, idx);
> > + pagecache_folio = filemap_lock_hugetlb_folio(vma, address);
> > if (IS_ERR(pagecache_folio))
> > pagecache_folio = NULL;
> > }
> > @@ -6258,7 +6262,7 @@ int hugetlb_mfill_atomic_pte(pte_t *dst_pte,
> > if (is_continue) {
> > ret = -EFAULT;
> > - folio = filemap_lock_folio(mapping, idx);
> > + folio = filemap_lock_hugetlb_folio(dst_vma, dst_addr);
> > if (IS_ERR(folio))
> > goto out;
> > folio_in_pagecache = true;
> > @@ -6350,7 +6354,7 @@ int hugetlb_mfill_atomic_pte(pte_t *dst_pte,
> > * hugetlb_fault_mutex_table that here must be hold by
> > * the caller.
> > */
> > - ret = hugetlb_add_to_page_cache(folio, mapping, idx);
> > + ret = hugetlb_add_to_page_cache(folio, dst_vma, mapping, dst_addr);
> > if (ret)
> > goto out_release_nounlock;
> > folio_in_pagecache = true;
>