Messages in this thread | | | Date | Wed, 31 Aug 2022 10:51:45 +0800 | Subject | Re: [PATCH 1/7] mm: introduce common struct mm_slot | From | Qi Zheng <> |
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On 2022/8/31 01:03, Yang Shi wrote: > On Mon, Aug 29, 2022 at 12:51 PM Andrew Morton > <akpm@linux-foundation.org> wrote: >> >> On Mon, 29 Aug 2022 22:30:49 +0800 Qi Zheng <zhengqi.arch@bytedance.com> wrote: >> >>> At present, both THP and KSM module have similar structures >>> mm_slot for organizing and recording the information required >>> for scanning mm, and each defines the following exactly the >>> same operation functions: >>> >>> - alloc_mm_slot >>> - free_mm_slot >>> - get_mm_slot >>> - insert_to_mm_slots_hash >>> >>> In order to de-duplicate these codes, this patch introduces a >>> common struct mm_slot, and subsequent patches will let THP and >>> KSM to use it. >> >> Seems like a good idea. >> >>> --- /dev/null >>> +++ b/mm/mm_slot.h >>> @@ -0,0 +1,55 @@ >>> +// SPDX-License-Identifier: GPL-2.0 >>> + >>> +#ifndef _LINUX_MM_SLOT_H >>> +#define _LINUX_MM_SLOT_H >>> + >>> +#include <linux/hashtable.h> >>> +#include <linux/slab.h> >>> + >>> +/* >>> + * struct mm_slot - hash lookup from mm to mm_slot >>> + * @hash: link to the mm_slots hash list >>> + * @mm_node: link into the mm_slots list >>> + * @mm: the mm that this information is valid for >>> + */ >>> +struct mm_slot { >>> + struct hlist_node hash; >>> + struct list_head mm_node; >>> + struct mm_struct *mm; >>> +}; >> >> It appears that the presence of an mm_struct in the hash list does not >> contribute to the mm_struct's refcount? That's somewhat unexpected. > > I didn't find time to look into the series yet, but when the > mm/mm_slot was added to the list, mmgrab() was definitely called if > this was not changed by the series.
Yeah, and this series does not change that.
> >> >> It would be helpful to add some words here describing the means by >> which a user of mm_slot would prevent the mm_struct from getting freed >> while on the list. I assume "caller must maintain a reference on the >> mm_struct while it remains on an mm_slot hash list"? >> >>> +#define mm_slot_entry(ptr, type, member) \ >>> + container_of(ptr, type, member) >>> + >>> +static inline void *alloc_mm_slot(struct kmem_cache *cache) >>> +{ >>> + if (!cache) /* initialization failed */ >>> + return NULL; >>> + return kmem_cache_zalloc(cache, GFP_KERNEL); >>> +} >>> + >>> +static inline void free_mm_slot(struct kmem_cache *cache, void *objp) >>> +{ >>> + kmem_cache_free(cache, objp); >>> +} >>> + >>> +#define get_mm_slot(_hashtable, _mm) \ >>> +({ \ >>> + struct mm_slot *tmp_slot, *mm_slot = NULL; \ >>> + \ >>> + hash_for_each_possible(_hashtable, tmp_slot, hash, (unsigned long)_mm) \ >>> + if (_mm == tmp_slot->mm) { \ >>> + mm_slot = tmp_slot; \ >>> + break; \ >>> + } \ >>> + \ >>> + mm_slot; \ >>> +}) >> >> Is there a reason why this must be implemented as a macro? That's >> preferable, although this may be overly large for inlining. mm/util.c >> might suit. >> >>> +#define insert_to_mm_slots_hash(_hashtable, _mm, _mm_slot) \ >>> +({ \ >>> + _mm_slot->mm = _mm; \ >>> + hash_add(_hashtable, &_mm_slot->hash, (unsigned long)_mm); \ >>> +}) >> >> Does this need to be a macro? >> >> >> And the naming. Can we please have >> >> mm_slot_entry >> mm_slot_alloc >> mm_slot_free >> mm_slot_get >> mm_slot_insert >> >> Also, "get" usually implies that a refcout is taken on the obtained >> object, so mm_slot_lookup() would be more appropriate. >>
-- Thanks, Qi
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