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Shutemov" , Mel Gorman , Suren Baghdasaryan , Michal Hocko , Richard Chang , linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 1/4] mm/page_isolation: make page isolation a standalone bit. 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Right on time. :) > > On Fri May 9, 2025 at 8:01 PM UTC, Zi Yan wrote: >> During page isolation, the original migratetype is overwritten, since >> MIGRATE_* are enums and stored in pageblock bitmaps. Change >> MIGRATE_ISOLATE to be stored a standalone bit, PB_migrate_isolate, like >> PB_migrate_skip, so that migratetype is not lost during pageblock >> isolation. pageblock bits needs to be word aligned, so expand >> the number of pageblock bits from 4 to 8 and make PB_migrate_isolate bit 7. > > Forgive my ignorance but can you help me confirm if I'm following this - > Do you just mean that NR_PAGEBLOCK_BITS must divide the word size? Or is > there something else going on here? You are right. NR_PAGEBLOCK_BITS must divide the word size. I will fix the commit log in the next version. > >> +#ifdef CONFIG_MEMORY_ISOLATION >> + PB_migrate_isolate = 7, /* If set the block is isolated */ >> + /* set it to 7 to make pageblock bit word aligned */ I will fix this comment too. >> +#endif > > I feel I'm always just asking for commentary so please feel free to > complain if this is annoying. But I think it would be worth adding the > context from the commit message into the code here (or somewhere else), > e.g: > > /* > * Page isolation is represented with a separate bit, so that the other > * bits can store the migratetype that the block had before it was > * isolated. > */ > > Just adding in that detail about the intent will help readers a lot IMO. Sure. Will add it. > >> >> +unsigned long get_pageblock_migratetype(const struct page *page) >> +{ >> + unsigned long flags; >> + >> + flags = get_pfnblock_flags_mask(page, page_to_pfn(page), >> + MIGRATETYPE_MASK); >> +#ifdef CONFIG_MEMORY_ISOLATION >> + if (flags & PB_migrate_isolate_bit) >> + return MIGRATE_ISOLATE; >> +#endif >> + return flags; >> +} > > Can we just do get_pageblock_migratetype(page, page_to_pfn(page)) here? Based on my observation, the callers all have page and pfn, so using the current implementation would save a call to page_to_pfn(). I can add a comment to this function. /* * Use get_pageblock_migratetype() if caller already has both @page and @pfn * to save a call to page_to_pfn(). */ > >> static __always_inline int get_pfnblock_migratetype(const struct page *page, >> unsigned long pfn) >> { >> - return get_pfnblock_flags_mask(page, pfn, MIGRATETYPE_MASK); >> + unsigned long flags; >> + >> + flags = get_pfnblock_flags_mask(page, pfn, >> + MIGRATETYPE_MASK); >> +#ifdef CONFIG_MEMORY_ISOLATION >> + if (flags & PB_migrate_isolate_bit) >> + return MIGRATE_ISOLATE; >> +#endif >> + return flags; >> } Best Regards, Yan, Zi