| Message ID | 20220704013312.2415700-2-naoya.horiguchi@linux.dev (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm, hwpoison: enable 1GB hugepage support (v4) | expand |
On 2022/7/4 9:33, Naoya Horiguchi wrote: > From: Naoya Horiguchi <naoya.horiguchi@nec.com> > > I found a weird state of 1GB hugepage pool, caused by the following > procedure: > > - run a process reserving all free 1GB hugepages, > - shrink free 1GB hugepage pool to zero (i.e. writing 0 to > /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages), then > - kill the reserving process. > > , then all the hugepages are free *and* surplus at the same time. > > $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages > 3 > $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/free_hugepages > 3 > $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/resv_hugepages > 0 > $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/surplus_hugepages > 3 > > This state is resolved by reserving and allocating the pages then > freeing them again, so this seems not to result in serious problem. > But it's a little surprising (shrinking pool suddenly fails). > > This behavior is caused by hstate_is_gigantic() check in > return_unused_surplus_pages(). This was introduced so long ago in 2008 > by commit aa888a74977a ("hugetlb: support larger than MAX_ORDER"), and > at that time the gigantic pages were not supposed to be allocated/freed > at run-time. Now kernel can support runtime allocation/free, so let's > check gigantic_page_runtime_supported() together. > > Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com> This patch looks good to me with a few question below. > --- > v2 -> v3: > - Fixed typo in patch description, > - add !gigantic_page_runtime_supported() check instead of removing > hstate_is_gigantic() check (suggested by Miaohe and Muchun) > - add a few more !gigantic_page_runtime_supported() check in > set_max_huge_pages() (by Mike). > --- > mm/hugetlb.c | 19 ++++++++++++++++--- > 1 file changed, 16 insertions(+), 3 deletions(-) > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index 2a554f006255..bdc4499f324b 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -2432,8 +2432,7 @@ static void return_unused_surplus_pages(struct hstate *h, > /* Uncommit the reservation */ > h->resv_huge_pages -= unused_resv_pages; > > - /* Cannot return gigantic pages currently */ > - if (hstate_is_gigantic(h)) > + if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported()) > goto out; > > /* > @@ -3315,7 +3314,8 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid, > * the user tries to allocate gigantic pages but let the user free the > * boottime allocated gigantic pages. > */ > - if (hstate_is_gigantic(h) && !IS_ENABLED(CONFIG_CONTIG_ALLOC)) { > + if (hstate_is_gigantic(h) && (!IS_ENABLED(CONFIG_CONTIG_ALLOC) || > + !gigantic_page_runtime_supported())) { > if (count > persistent_huge_pages(h)) { > spin_unlock_irq(&hugetlb_lock); > mutex_unlock(&h->resize_lock); > @@ -3363,6 +3363,19 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid, > goto out; > } > > + /* > + * We can not decrease gigantic pool size if runtime modification > + * is not supported. > + */ > + if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported()) { > + if (count < persistent_huge_pages(h)) { > + spin_unlock_irq(&hugetlb_lock); > + mutex_unlock(&h->resize_lock); > + NODEMASK_FREE(node_alloc_noretry); > + return -EINVAL; > + } > + } With above change, we're not allowed to decrease the pool size now. But it was allowed previously even if !gigantic_page_runtime_supported. Does this will break user? And it seems it's not allowed to adjust the max_huge_pages now if !gigantic_page_runtime_supported for gigantic huge page. Should we just return for such case as there should be nothing to do now? Or am I miss something? Thanks! > + > /* > * Decrease the pool size > * First return free pages to the buddy allocator (being careful >
On Tue, Jul 05, 2022 at 10:16:39AM +0800, Miaohe Lin wrote: > On 2022/7/4 9:33, Naoya Horiguchi wrote: > > From: Naoya Horiguchi <naoya.horiguchi@nec.com> > > > > I found a weird state of 1GB hugepage pool, caused by the following > > procedure: > > > > - run a process reserving all free 1GB hugepages, > > - shrink free 1GB hugepage pool to zero (i.e. writing 0 to > > /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages), then > > - kill the reserving process. > > > > , then all the hugepages are free *and* surplus at the same time. > > > > $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages > > 3 > > $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/free_hugepages > > 3 > > $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/resv_hugepages > > 0 > > $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/surplus_hugepages > > 3 > > > > This state is resolved by reserving and allocating the pages then > > freeing them again, so this seems not to result in serious problem. > > But it's a little surprising (shrinking pool suddenly fails). > > > > This behavior is caused by hstate_is_gigantic() check in > > return_unused_surplus_pages(). This was introduced so long ago in 2008 > > by commit aa888a74977a ("hugetlb: support larger than MAX_ORDER"), and > > at that time the gigantic pages were not supposed to be allocated/freed > > at run-time. Now kernel can support runtime allocation/free, so let's > > check gigantic_page_runtime_supported() together. > > > > Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com> > > This patch looks good to me with a few question below. Thank you for reviewing. > > > --- > > v2 -> v3: > > - Fixed typo in patch description, > > - add !gigantic_page_runtime_supported() check instead of removing > > hstate_is_gigantic() check (suggested by Miaohe and Muchun) > > - add a few more !gigantic_page_runtime_supported() check in > > set_max_huge_pages() (by Mike). > > --- > > mm/hugetlb.c | 19 ++++++++++++++++--- > > 1 file changed, 16 insertions(+), 3 deletions(-) > > > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > > index 2a554f006255..bdc4499f324b 100644 > > --- a/mm/hugetlb.c > > +++ b/mm/hugetlb.c > > @@ -2432,8 +2432,7 @@ static void return_unused_surplus_pages(struct hstate *h, > > /* Uncommit the reservation */ > > h->resv_huge_pages -= unused_resv_pages; > > > > - /* Cannot return gigantic pages currently */ > > - if (hstate_is_gigantic(h)) > > + if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported()) > > goto out; > > > > /* > > @@ -3315,7 +3314,8 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid, > > * the user tries to allocate gigantic pages but let the user free the > > * boottime allocated gigantic pages. > > */ > > - if (hstate_is_gigantic(h) && !IS_ENABLED(CONFIG_CONTIG_ALLOC)) { > > + if (hstate_is_gigantic(h) && (!IS_ENABLED(CONFIG_CONTIG_ALLOC) || > > + !gigantic_page_runtime_supported())) { > > if (count > persistent_huge_pages(h)) { > > spin_unlock_irq(&hugetlb_lock); > > mutex_unlock(&h->resize_lock); > > @@ -3363,6 +3363,19 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid, > > goto out; > > } > > > > + /* > > + * We can not decrease gigantic pool size if runtime modification > > + * is not supported. > > + */ > > + if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported()) { > > + if (count < persistent_huge_pages(h)) { > > + spin_unlock_irq(&hugetlb_lock); > > + mutex_unlock(&h->resize_lock); > > + NODEMASK_FREE(node_alloc_noretry); > > + return -EINVAL; > > + } > > + } > > With above change, we're not allowed to decrease the pool size now. But it was allowed previously > even if !gigantic_page_runtime_supported. Does this will break user? Yes, it does. I might get the wrong idea about the definition of gigantic_page_runtime_supported(), which shows that runtime pool *extension* is supported or not (implying that pool shrinking is always possible). If this is right, this new if-block is not necessary. > > And it seems it's not allowed to adjust the max_huge_pages now if !gigantic_page_runtime_supported > for gigantic huge page. Should we just return for such case as there should be nothing to do now? > Or am I miss something? If pool shrinking is always allowed, we need uptdate max_huge_pages so, the above if-block should have "goto out;", but it will be removed anyway so we don't have to care for it. Thank you for the valuable comment. - Naoya Horiguchi
On 2022/7/5 14:39, HORIGUCHI NAOYA(堀口 直也) wrote: > On Tue, Jul 05, 2022 at 10:16:39AM +0800, Miaohe Lin wrote: >> On 2022/7/4 9:33, Naoya Horiguchi wrote: >>> From: Naoya Horiguchi <naoya.horiguchi@nec.com> >>> >>> I found a weird state of 1GB hugepage pool, caused by the following >>> procedure: >>> >>> - run a process reserving all free 1GB hugepages, >>> - shrink free 1GB hugepage pool to zero (i.e. writing 0 to >>> /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages), then >>> - kill the reserving process. >>> >>> , then all the hugepages are free *and* surplus at the same time. >>> >>> $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages >>> 3 >>> $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/free_hugepages >>> 3 >>> $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/resv_hugepages >>> 0 >>> $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/surplus_hugepages >>> 3 >>> >>> This state is resolved by reserving and allocating the pages then >>> freeing them again, so this seems not to result in serious problem. >>> But it's a little surprising (shrinking pool suddenly fails). >>> >>> This behavior is caused by hstate_is_gigantic() check in >>> return_unused_surplus_pages(). This was introduced so long ago in 2008 >>> by commit aa888a74977a ("hugetlb: support larger than MAX_ORDER"), and >>> at that time the gigantic pages were not supposed to be allocated/freed >>> at run-time. Now kernel can support runtime allocation/free, so let's >>> check gigantic_page_runtime_supported() together. >>> >>> Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com> >> >> This patch looks good to me with a few question below. > > Thank you for reviewing. > >> >>> --- >>> v2 -> v3: >>> - Fixed typo in patch description, >>> - add !gigantic_page_runtime_supported() check instead of removing >>> hstate_is_gigantic() check (suggested by Miaohe and Muchun) >>> - add a few more !gigantic_page_runtime_supported() check in >>> set_max_huge_pages() (by Mike). >>> --- >>> mm/hugetlb.c | 19 ++++++++++++++++--- >>> 1 file changed, 16 insertions(+), 3 deletions(-) >>> >>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c >>> index 2a554f006255..bdc4499f324b 100644 >>> --- a/mm/hugetlb.c >>> +++ b/mm/hugetlb.c >>> @@ -2432,8 +2432,7 @@ static void return_unused_surplus_pages(struct hstate *h, >>> /* Uncommit the reservation */ >>> h->resv_huge_pages -= unused_resv_pages; >>> >>> - /* Cannot return gigantic pages currently */ >>> - if (hstate_is_gigantic(h)) >>> + if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported()) >>> goto out; >>> >>> /* >>> @@ -3315,7 +3314,8 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid, >>> * the user tries to allocate gigantic pages but let the user free the >>> * boottime allocated gigantic pages. >>> */ >>> - if (hstate_is_gigantic(h) && !IS_ENABLED(CONFIG_CONTIG_ALLOC)) { >>> + if (hstate_is_gigantic(h) && (!IS_ENABLED(CONFIG_CONTIG_ALLOC) || >>> + !gigantic_page_runtime_supported())) { >>> if (count > persistent_huge_pages(h)) { >>> spin_unlock_irq(&hugetlb_lock); >>> mutex_unlock(&h->resize_lock); >>> @@ -3363,6 +3363,19 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid, >>> goto out; >>> } >>> >>> + /* >>> + * We can not decrease gigantic pool size if runtime modification >>> + * is not supported. >>> + */ >>> + if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported()) { >>> + if (count < persistent_huge_pages(h)) { >>> + spin_unlock_irq(&hugetlb_lock); >>> + mutex_unlock(&h->resize_lock); >>> + NODEMASK_FREE(node_alloc_noretry); >>> + return -EINVAL; >>> + } >>> + } >> >> With above change, we're not allowed to decrease the pool size now. But it was allowed previously >> even if !gigantic_page_runtime_supported. Does this will break user? > > Yes, it does. I might get the wrong idea about the definition of > gigantic_page_runtime_supported(), which shows that runtime pool *extension* > is supported or not (implying that pool shrinking is always possible). > If this is right, this new if-block is not necessary. I tend to remove above new if-block to keep pool shrinking available. Thanks. > >> >> And it seems it's not allowed to adjust the max_huge_pages now if !gigantic_page_runtime_supported >> for gigantic huge page. Should we just return for such case as there should be nothing to do now? >> Or am I miss something? > > If pool shrinking is always allowed, we need uptdate max_huge_pages so, > the above if-block should have "goto out;", but it will be removed anyway > so we don't have to care for it. > > Thank you for the valuable comment. > > - Naoya Horiguchi >
On 07/06/22 11:04, Miaohe Lin wrote: > On 2022/7/5 14:39, HORIGUCHI NAOYA(堀口 直也) wrote: > > On Tue, Jul 05, 2022 at 10:16:39AM +0800, Miaohe Lin wrote: > >> On 2022/7/4 9:33, Naoya Horiguchi wrote: > >>> From: Naoya Horiguchi <naoya.horiguchi@nec.com> > >>> > >>> I found a weird state of 1GB hugepage pool, caused by the following > >>> procedure: > >>> > >>> - run a process reserving all free 1GB hugepages, > >>> - shrink free 1GB hugepage pool to zero (i.e. writing 0 to > >>> /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages), then > >>> - kill the reserving process. > >>> > >>> , then all the hugepages are free *and* surplus at the same time. > >>> > >>> $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages > >>> 3 > >>> $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/free_hugepages > >>> 3 > >>> $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/resv_hugepages > >>> 0 > >>> $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/surplus_hugepages > >>> 3 > >>> > >>> This state is resolved by reserving and allocating the pages then > >>> freeing them again, so this seems not to result in serious problem. > >>> But it's a little surprising (shrinking pool suddenly fails). > >>> > >>> This behavior is caused by hstate_is_gigantic() check in > >>> return_unused_surplus_pages(). This was introduced so long ago in 2008 > >>> by commit aa888a74977a ("hugetlb: support larger than MAX_ORDER"), and > >>> at that time the gigantic pages were not supposed to be allocated/freed > >>> at run-time. Now kernel can support runtime allocation/free, so let's > >>> check gigantic_page_runtime_supported() together. > >>> > >>> Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com> > >> > >> This patch looks good to me with a few question below. > > > > Thank you for reviewing. > > > >> > >>> --- > >>> v2 -> v3: > >>> - Fixed typo in patch description, > >>> - add !gigantic_page_runtime_supported() check instead of removing > >>> hstate_is_gigantic() check (suggested by Miaohe and Muchun) > >>> - add a few more !gigantic_page_runtime_supported() check in > >>> set_max_huge_pages() (by Mike). > >>> --- > >>> mm/hugetlb.c | 19 ++++++++++++++++--- > >>> 1 file changed, 16 insertions(+), 3 deletions(-) > >>> > >>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c > >>> index 2a554f006255..bdc4499f324b 100644 > >>> --- a/mm/hugetlb.c > >>> +++ b/mm/hugetlb.c > >>> @@ -2432,8 +2432,7 @@ static void return_unused_surplus_pages(struct hstate *h, > >>> /* Uncommit the reservation */ > >>> h->resv_huge_pages -= unused_resv_pages; > >>> > >>> - /* Cannot return gigantic pages currently */ > >>> - if (hstate_is_gigantic(h)) > >>> + if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported()) > >>> goto out; > >>> > >>> /* > >>> @@ -3315,7 +3314,8 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid, > >>> * the user tries to allocate gigantic pages but let the user free the > >>> * boottime allocated gigantic pages. > >>> */ > >>> - if (hstate_is_gigantic(h) && !IS_ENABLED(CONFIG_CONTIG_ALLOC)) { > >>> + if (hstate_is_gigantic(h) && (!IS_ENABLED(CONFIG_CONTIG_ALLOC) || > >>> + !gigantic_page_runtime_supported())) { > >>> if (count > persistent_huge_pages(h)) { > >>> spin_unlock_irq(&hugetlb_lock); > >>> mutex_unlock(&h->resize_lock); > >>> @@ -3363,6 +3363,19 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid, > >>> goto out; > >>> } > >>> > >>> + /* > >>> + * We can not decrease gigantic pool size if runtime modification > >>> + * is not supported. > >>> + */ > >>> + if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported()) { > >>> + if (count < persistent_huge_pages(h)) { > >>> + spin_unlock_irq(&hugetlb_lock); > >>> + mutex_unlock(&h->resize_lock); > >>> + NODEMASK_FREE(node_alloc_noretry); > >>> + return -EINVAL; > >>> + } > >>> + } > >> > >> With above change, we're not allowed to decrease the pool size now. But it was allowed previously > >> even if !gigantic_page_runtime_supported. Does this will break user? > > > > Yes, it does. I might get the wrong idea about the definition of > > gigantic_page_runtime_supported(), which shows that runtime pool *extension* > > is supported or not (implying that pool shrinking is always possible). > > If this is right, this new if-block is not necessary. > > I tend to remove above new if-block to keep pool shrinking available. > Not sure I am following the questions. Take a look at __update_and_free_page which will refuse to 'free' a gigantic page if !gigantic_page_runtime_supported. I 'think' attempting to shrink the pool when !gigantic_page_runtime_supported will result in leaking gigantic pages. i.e. Memory will remain allocated for the gigantic page, but it can not be used. I can take a closer look during my tomorrow. IIRC, the only way gigantic_page_runtime_supported is not set to day is in the case of powerpc using 16GB pages allocated/managed by firmware.
On 07/04/22 10:33, Naoya Horiguchi wrote: > From: Naoya Horiguchi <naoya.horiguchi@nec.com> > > I found a weird state of 1GB hugepage pool, caused by the following > procedure: > > - run a process reserving all free 1GB hugepages, > - shrink free 1GB hugepage pool to zero (i.e. writing 0 to > /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages), then > - kill the reserving process. > > , then all the hugepages are free *and* surplus at the same time. > > $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages > 3 > $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/free_hugepages > 3 > $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/resv_hugepages > 0 > $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/surplus_hugepages > 3 > > This state is resolved by reserving and allocating the pages then > freeing them again, so this seems not to result in serious problem. > But it's a little surprising (shrinking pool suddenly fails). > > This behavior is caused by hstate_is_gigantic() check in > return_unused_surplus_pages(). This was introduced so long ago in 2008 > by commit aa888a74977a ("hugetlb: support larger than MAX_ORDER"), and > at that time the gigantic pages were not supposed to be allocated/freed > at run-time. Now kernel can support runtime allocation/free, so let's > check gigantic_page_runtime_supported() together. > > Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com> > --- > v2 -> v3: > - Fixed typo in patch description, > - add !gigantic_page_runtime_supported() check instead of removing > hstate_is_gigantic() check (suggested by Miaohe and Muchun) > - add a few more !gigantic_page_runtime_supported() check in > set_max_huge_pages() (by Mike). Hi Naoya, My apologies for suggesting the above checks in set_max_huge_pages(). set_max_huge_pages is only called from __nr_hugepages_store_common. At the very beginning of __nr_hugepages_store_common is this: if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported()) return -EINVAL; So, those extra checks in set_max_huge_pages are unnecessary. Sorry!
On Wed, Jul 06, 2022 at 02:51:00PM -0700, Mike Kravetz wrote: > On 07/04/22 10:33, Naoya Horiguchi wrote: > > From: Naoya Horiguchi <naoya.horiguchi@nec.com> > > > > I found a weird state of 1GB hugepage pool, caused by the following > > procedure: > > > > - run a process reserving all free 1GB hugepages, > > - shrink free 1GB hugepage pool to zero (i.e. writing 0 to > > /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages), then > > - kill the reserving process. > > > > , then all the hugepages are free *and* surplus at the same time. > > > > $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages > > 3 > > $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/free_hugepages > > 3 > > $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/resv_hugepages > > 0 > > $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/surplus_hugepages > > 3 > > > > This state is resolved by reserving and allocating the pages then > > freeing them again, so this seems not to result in serious problem. > > But it's a little surprising (shrinking pool suddenly fails). > > > > This behavior is caused by hstate_is_gigantic() check in > > return_unused_surplus_pages(). This was introduced so long ago in 2008 > > by commit aa888a74977a ("hugetlb: support larger than MAX_ORDER"), and > > at that time the gigantic pages were not supposed to be allocated/freed > > at run-time. Now kernel can support runtime allocation/free, so let's > > check gigantic_page_runtime_supported() together. > > > > Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com> > > --- > > v2 -> v3: > > - Fixed typo in patch description, > > - add !gigantic_page_runtime_supported() check instead of removing > > hstate_is_gigantic() check (suggested by Miaohe and Muchun) > > - add a few more !gigantic_page_runtime_supported() check in > > set_max_huge_pages() (by Mike). > > Hi Naoya, > > My apologies for suggesting the above checks in set_max_huge_pages(). > set_max_huge_pages is only called from __nr_hugepages_store_common. > At the very beginning of __nr_hugepages_store_common is this: > > if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported()) > return -EINVAL; > > So, those extra checks in set_max_huge_pages are unnecessary. Sorry! OK, so I'll drop both checks, thank you. - Naoya Horiguchi
On 2022/7/6 11:22, Mike Kravetz wrote: > On 07/06/22 11:04, Miaohe Lin wrote: >> On 2022/7/5 14:39, HORIGUCHI NAOYA(堀口 直也) wrote: >>> On Tue, Jul 05, 2022 at 10:16:39AM +0800, Miaohe Lin wrote: >>>> On 2022/7/4 9:33, Naoya Horiguchi wrote: >>>>> From: Naoya Horiguchi <naoya.horiguchi@nec.com> >>>>> >>>>> I found a weird state of 1GB hugepage pool, caused by the following >>>>> procedure: >>>>> >>>>> - run a process reserving all free 1GB hugepages, >>>>> - shrink free 1GB hugepage pool to zero (i.e. writing 0 to >>>>> /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages), then >>>>> - kill the reserving process. >>>>> >>>>> , then all the hugepages are free *and* surplus at the same time. >>>>> >>>>> $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages >>>>> 3 >>>>> $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/free_hugepages >>>>> 3 >>>>> $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/resv_hugepages >>>>> 0 >>>>> $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/surplus_hugepages >>>>> 3 >>>>> >>>>> This state is resolved by reserving and allocating the pages then >>>>> freeing them again, so this seems not to result in serious problem. >>>>> But it's a little surprising (shrinking pool suddenly fails). >>>>> >>>>> This behavior is caused by hstate_is_gigantic() check in >>>>> return_unused_surplus_pages(). This was introduced so long ago in 2008 >>>>> by commit aa888a74977a ("hugetlb: support larger than MAX_ORDER"), and >>>>> at that time the gigantic pages were not supposed to be allocated/freed >>>>> at run-time. Now kernel can support runtime allocation/free, so let's >>>>> check gigantic_page_runtime_supported() together. >>>>> >>>>> Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com> >>>> >>>> This patch looks good to me with a few question below. >>> >>> Thank you for reviewing. >>> >>>> >>>>> --- >>>>> v2 -> v3: >>>>> - Fixed typo in patch description, >>>>> - add !gigantic_page_runtime_supported() check instead of removing >>>>> hstate_is_gigantic() check (suggested by Miaohe and Muchun) >>>>> - add a few more !gigantic_page_runtime_supported() check in >>>>> set_max_huge_pages() (by Mike). >>>>> --- >>>>> mm/hugetlb.c | 19 ++++++++++++++++--- >>>>> 1 file changed, 16 insertions(+), 3 deletions(-) >>>>> >>>>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c >>>>> index 2a554f006255..bdc4499f324b 100644 >>>>> --- a/mm/hugetlb.c >>>>> +++ b/mm/hugetlb.c >>>>> @@ -2432,8 +2432,7 @@ static void return_unused_surplus_pages(struct hstate *h, >>>>> /* Uncommit the reservation */ >>>>> h->resv_huge_pages -= unused_resv_pages; >>>>> >>>>> - /* Cannot return gigantic pages currently */ >>>>> - if (hstate_is_gigantic(h)) >>>>> + if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported()) >>>>> goto out; >>>>> >>>>> /* >>>>> @@ -3315,7 +3314,8 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid, >>>>> * the user tries to allocate gigantic pages but let the user free the >>>>> * boottime allocated gigantic pages. >>>>> */ >>>>> - if (hstate_is_gigantic(h) && !IS_ENABLED(CONFIG_CONTIG_ALLOC)) { >>>>> + if (hstate_is_gigantic(h) && (!IS_ENABLED(CONFIG_CONTIG_ALLOC) || >>>>> + !gigantic_page_runtime_supported())) { >>>>> if (count > persistent_huge_pages(h)) { >>>>> spin_unlock_irq(&hugetlb_lock); >>>>> mutex_unlock(&h->resize_lock); >>>>> @@ -3363,6 +3363,19 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid, >>>>> goto out; >>>>> } >>>>> >>>>> + /* >>>>> + * We can not decrease gigantic pool size if runtime modification >>>>> + * is not supported. >>>>> + */ >>>>> + if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported()) { >>>>> + if (count < persistent_huge_pages(h)) { >>>>> + spin_unlock_irq(&hugetlb_lock); >>>>> + mutex_unlock(&h->resize_lock); >>>>> + NODEMASK_FREE(node_alloc_noretry); >>>>> + return -EINVAL; >>>>> + } >>>>> + } >>>> >>>> With above change, we're not allowed to decrease the pool size now. But it was allowed previously >>>> even if !gigantic_page_runtime_supported. Does this will break user? >>> >>> Yes, it does. I might get the wrong idea about the definition of >>> gigantic_page_runtime_supported(), which shows that runtime pool *extension* >>> is supported or not (implying that pool shrinking is always possible). >>> If this is right, this new if-block is not necessary. >> >> I tend to remove above new if-block to keep pool shrinking available. >> > > Not sure I am following the questions. > > Take a look at __update_and_free_page which will refuse to 'free' a > gigantic page if !gigantic_page_runtime_supported. I 'think' attempting > to shrink the pool when !gigantic_page_runtime_supported will result in > leaking gigantic pages. i.e. Memory will remain allocated for the It seems the commit 4eb0716e868e ("hugetlb: allow to free gigantic pages regardless of the configuration") adds the ability to free gigantic pages even if !gigantic_page_supported(). If the gigantic pages can't be freed due to gigantic_page_runtime_supported check if __update_and_free_page, there might be something need to do -- disallow trying to free gigantic pages when !gigantic_page_supported or succeeds to free gigantic pages regardless of gigantic_page_supported. Maybe I am missing something important. Add Alexandre to help confirm. Thanks! > gigantic page, but it can not be used. > > I can take a closer look during my tomorrow. > > IIRC, the only way gigantic_page_runtime_supported is not set to day is > in the case of powerpc using 16GB pages allocated/managed by firmware. >
diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 2a554f006255..bdc4499f324b 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -2432,8 +2432,7 @@ static void return_unused_surplus_pages(struct hstate *h, /* Uncommit the reservation */ h->resv_huge_pages -= unused_resv_pages; - /* Cannot return gigantic pages currently */ - if (hstate_is_gigantic(h)) + if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported()) goto out; /* @@ -3315,7 +3314,8 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid, * the user tries to allocate gigantic pages but let the user free the * boottime allocated gigantic pages. */ - if (hstate_is_gigantic(h) && !IS_ENABLED(CONFIG_CONTIG_ALLOC)) { + if (hstate_is_gigantic(h) && (!IS_ENABLED(CONFIG_CONTIG_ALLOC) || + !gigantic_page_runtime_supported())) { if (count > persistent_huge_pages(h)) { spin_unlock_irq(&hugetlb_lock); mutex_unlock(&h->resize_lock); @@ -3363,6 +3363,19 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid, goto out; } + /* + * We can not decrease gigantic pool size if runtime modification + * is not supported. + */ + if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported()) { + if (count < persistent_huge_pages(h)) { + spin_unlock_irq(&hugetlb_lock); + mutex_unlock(&h->resize_lock); + NODEMASK_FREE(node_alloc_noretry); + return -EINVAL; + } + } + /* * Decrease the pool size * First return free pages to the buddy allocator (being careful