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    SubjectRe: [RFC 1/5] mm, page_alloc: clean up pageset high and batch update
    On Mon, Sep 07, 2020 at 06:36:24PM +0200, Vlastimil Babka wrote:
    > Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

    > for_each_possible_cpu(cpu)
    > - setup_pageset(&per_cpu(boot_pageset, cpu), 0);
    > + setup_pageset(&per_cpu(boot_pageset, cpu));

    This is not really anything important but I realized we have like 7 functions
    messing with pcp lists, and everytime I try to follow them my head spins.

    Since setup_pageset is only being called here, could we replace it by the
    pageset_init and pageset_update?

    (As I said, not important and probably a matter of taste. I just think that
    having so many mini functions around is not always cool,
    e.g: setup_zone_pageset->zone_pageset_init)

    > -/*
    > - * pageset_set_high() sets the high water mark for hot per_cpu_pagelist
    > - * to the value high for the pageset p.
    > - */
    > -static void pageset_set_high(struct per_cpu_pageset *p,
    > - unsigned long high)
    > -{
    > - unsigned long batch = max(1UL, high / 4);
    > - if ((high / 4) > (PAGE_SHIFT * 8))
    > - batch = PAGE_SHIFT * 8;
    > -
    > - pageset_update(&p->pcp, high, batch);
    > + pageset_update(&p->pcp, 0, 1);
    > }

    Could we restore the comment we had in pageset_set_high, and maybe
    update it to match this new function? I think it would be useful.
    >
    > static void pageset_set_high_and_batch(struct zone *zone,
    > - struct per_cpu_pageset *pcp)
    > + struct per_cpu_pageset *p)
    > {
    > - if (percpu_pagelist_fraction)
    > - pageset_set_high(pcp,
    > - (zone_managed_pages(zone) /
    > - percpu_pagelist_fraction));
    > - else
    > - pageset_set_batch(pcp, zone_batchsize(zone));
    > + unsigned long new_high;
    > + unsigned long new_batch;
    > + int fraction = READ_ONCE(percpu_pagelist_fraction);

    Why the READ_ONCE? In case there is a parallel update so things to get
    messed up?

    as I said, I'd appreciate a comment in pageset_set_high_and_batch to be
    restored and updated, otherwise:

    Reviewed-by: Oscar Salvador <osalvador@suse.de>

    Thanks

    --
    Oscar Salvador
    SUSE L3

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